A fouled or black spark plug is a real pain, symptoms vary by how badly the plug is fouled. But you can be sure the engine is struggling to perform and ATV is frustrating to ride. A black or fouled ATV spark plug is a very common ATV issue and now the good news, it’s usually a five-minute fix. I’m a mechanic and you are in the correct place, a few minutes from now she’ll be revving clean.

A fouled or black ATV spark plug is a sign the engine is running fuel-rich and that’s commonly caused by:

• Blocked air filter
• Incorrect choke use or fault
• Ignition system fault
• Fuel system fault
• Mechanical fault

In this post you’ll learn the most common causes of a black or fouled ATV spark plug and what you can do to fix them right now.

Black ATV Spark Plug Common Causes

Before beginning the diagnosis process it’s worth making some basic checks like oil level and oil type. Too much engine oil will cause the engine to burn off the excess oil and that can cause an oily black plug. Also using the incorrect oil type may cause excessive oil consumption also causing plug fouling.

A black spark plug means your engine is running rich. Rich means your engine is getting too much gas in relation to the amount of air (oxygen) it’s receiving. Your ATV engine likes to run with 14.7 parts air (oxygen) to one part gas, it’s called the AFR or Air Fuel Ratio.

Your ATV’s carburetor is responsible for mixing and maintaining the AFR. When either the airflow to the engine or the gas supply is out of spec, the engine won’t operate at its optimum or maybe won’t run at all.

AFR conditions may be described as:

Rich – An engine that receives too much gas or not enough air is said to be running rich.

Lean – Conversely, an engine that gets too much air or not enough gas is said to run lean.

Both conditions are bad, but since your ATV plug is black I suspect your engine is running rich. Rich as you know means your engine is either getting too much gas or not enough air.

A common cause of a rich running engine and consequently a black plug is a dirty air filter. And so that’s what we cover first in the list of common rich running causes below.

Blocked Air Filter

A blocked air filter as you know restricts airflow to the engine and that may cause a rich condition. An air filter is easy to check since most manufacturers employ toolless access. And since it’s a common cause and it’s so easy to check we’ll do that first.

The fix – Simple enough, right, clean or replace the filter. Foam filters are washable in detergent but sure to allow them to dry completely and if your filter is a performance filter it will need to be oiled.

And yes you will need to use a special air filter, filter oil is sticky it’s formulated to catch and trap fine dust particles that would otherwise sandblast the interior of your motor.

Choke

Incorrect Choke Use – Riding with the choke partially “On” will create a rich condition and that may cause the plug to become black. I understand some ATVs run a little better with the choke “On” and that’s a sign of a possible carburetor blockage or the carburetor requires adjustment.

Although the engine runs better with the choke “On” it does run the risk of washing the protective oil coat from the cylinder walls and diluting the engine oil.

Choke Stuck “On” – A choke sticking in the “On” or partially “On” position will create a rich condition and as mentioned above, wash the cylinder and contaminate the engine oil. This is a real risk of seizing the engine, and a seized engine as you know is beyond economic repair.

To check choke operation you’ll need to remove the airbox pipework so as to gain access to the choke plate (if fitted).

Operating the choke and observing its “Off” open position. Some choke systems are operated by cable and may require adjustment.

This test won’t apply to more modern ATVs with an electric choke fitted.

Ignition System Fault

There are many components in the ignition system all of which could in theory cause a rich condition by intermittingly breaking down. However the most likely component in the ignition system to cause a black spark plug is the plug itself, and that’s what we’ll look at next.

Incorrect Plug Gap – A spark plug is a tough component and modern plugs tend to last a ton longer than previous generations. That said they do require a little maintenance and replacing. Most ATV engine makers recommend a plug replacement every two years and a plug clean and re-gap every three months.

Gapping the plug refers to the gap between the positive and negative electrodes.

An excessive plug gap causes misfiring and a black spark plug, in addition, it places excessive stress on the ignition system and promotes excessive amp draw.

The fix – Check and gapping the spark plug takes just a few minutes once the plug is removed. Alternatively, replace the spark plug, they come already gapped.

To gap a plug, you’ll need a plug socket and ratchet, a feeler gauge, and pliers. Check your engine maker’s recommended gap spec, (usually about 0.7-0.8mm (0.028-0.031)) select the correct feeler gauge blade and place it in the plug gap. To close the gap, use the pliers to tap on the negative electrode.

To open the gap, grip the negative electrode with the pliers and open it slightly.

Re-adjust as necessary.

Wrong Spark Plug – This one is self-explanatory, well almost. Plugs are graded by heat range, meaning they have an optimum temperature of operation. A plug is designed to get hot enough to burn off plug contaminates that naturally form and contaminate the plug.

A plug that’s too hot will pre-ignite the fuel mixture and that’s damaging to the engine. Conversely, a plug that’s too cold won’t ever get hot enough to burn off those carbon deposits and results in a black plug.

As a rough guide, a brown plug insulator (discolored insulator around central electrode) suggests the plug is correct and all is well inside the combustion chamber.

An unmarked or dark-colored insulator suggests there’s a problem.

The fix – Check the plug spec in your driver’s manual or check the spec online.

Ignition Electrical System Fault – An intermittent electrical system fault is a pain in the jacksie and is a contender for a rich condition. To be fair an intermittent electrical issue should make itself known, misfiring and loss of power and or stalling.

Fitting a Spark Plug

When fitting a spark plug it is important to tighten it correctly. Both too tight and too loose are bad.

As a guide, tighten a used washered spark plug 1/8 to 1/4 turn after the plug seats. Tighten a new washered plug 1/2 turn after the plug seats.

Fuel System Fault

The system includes the following components – the gas itself, gas tank, gas filter, fuel pump (if fitted), and carburetor.

Bad Gas – The gas itself is a common cause of misfiring and a black plug. Using unapproved, low-quality gas, contaminated gas, or just stale gas will cause the engine to misfire, and that as you know causes a black plug. Draining the fuel system removing the gas and adding a fuel stabilizer will prevent the gas from going stale in the future.

Most ATVs are happy with 87 octane or 10% ethanol blend but when using ethanol use a gas stabilizer mix to help guard against moisture.

Incorrect Carburetor Mix – The carburetor employs an adjustment screw where the air to fuel ratio can be adjusted. It isn’t uncommon for carb screws to move out of adjustment. Adjusting isn’t difficult, but you will need to check the location of your mix screw(s).

Mechanical Fault

A mechanical fault has a place on this list also. Excessive oil inside the cylinder will result in a contaminated spark plug, however, this is usually accompanied by blue smoke.

Worn Oil Rings – Worn oil rings will allow oil to sneak past the rings and that will contaminate the spark plug.

Worn Valve Stem Oil Seals – Hard, worn, or cracked oil seals will allow oil into the cylinder and you guessed it contaminate the spark plug.

You may find the following posts helpful:

Air cooled ATV white smoke

Can I ride with choke on?

How to start an ATV in cold weather

ATV won’t start after washing

ATV won’t pull start

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post Why is ATV Spark Plug Black? Easy fix! appeared first on ATVFixed.com.

White smoke from the tailpipe looks serious, but usually, it’s a simple problem, easily fixed.

Top 4 reasons for white smoke from an air-cooled ATV include:

1. Too much oil
2. Wrong oil type
3. Contaminated gas
4. Condensation

By the end of this post, you’ll understand the root causes of white smoke from an air-cooled ATV and what you can do to fix them.

1 Too Much Oil

Mixing gas and oil is mission-critical to a two-stroke engine. As you know, a two-stroke doesn’t have a sump filled with oil; instead, the engine depends on the two-cycle oil to lubricate and cool the moving parts.

Without the oil, the engine would seize solid within minutes. Too little oil in the gas mix risks seizure also. Being over-generous with the oil is bad too. It causes the motor to run lean, and a lean engine runs fast and hot.

In addition, excess oil accumulates in the crankcase and is eventually burnt in the combustion chamber, where it causes a ton of white smoke. If your bike is a two-stroke, its carburetor is calibrated (jetted) to burn oil and fuel to a specified ratio, for example, 32:1. Deviating from this very precise ratio can cause your engine to run lean or rich. Both will shorten the life of your engine.

If your bike is a four-stroke simply overfilling with oil is the more usual cause of white smoke and is easily fixed, drain off the excess oil. Most single cylinder ATVs will take approx. 2.5 US qts of oil.

2 Wrong Oil Type

Using the wrong type of oil is a common mistake. Regular engine oil is too heavy for burning in a two-stroke engine and will produce plooms of white smoke. Engine oil won’t protect your engine either. It doesn’t thoroughly mix with gas, and your engine will be damaged by friction and heat. Even a short period of operation could cause damage.

Using the wrong grade oil in a four-stroke engine may cause some bikes issues. Running a bike on a very light fully synthetic may cause excessive oil consumption. Best to check your owner manual for the oil type recommended, despite what lots of folks say all oil is not the same.

You will need to be mindful of operating in extreme temperatures.

If you live and play in sub-zero temps, you may need to use thinner oil which as you know flows more easily in cold temps. See chart.

Common oil grades include – 5W30, 10W30, 10W40, 15W40, 20W40, 20W50.

3 Contaminated Gas

Bad gas will cause any engine to act up. Regular gas goes stale after three months and blended behind to go off in as little as one month under certain conditions.

Blended gas

Fuels with higher alcohol content generally aren’t good for two-stroke engines. Ethanol blended fuels like E15 burn hotter, and heat is the enemy of any motor. 87 octane regular gas is preferred.

Blended gas is bad open to atmosphere fuel systems and a gas stabilizer should be used to help keep the gas fresh and to protect the fuel system from gumming, a common winter storage issue.

You’ll find the gas stabilizer I recommend here on the ATV parts page.

Water

Riding through water will cause steam on the exhaust, and if the airbox gets a drink, the engine will ingest it and turn it into steam. So, if you’ve been playing in the water, check that airbox, its drain, and air filter.

Drain the carburetor gas bowl too.

Not Gas

Accidentally and unknowingly filling the gas tank with diesel, white spirits, thinners, or I’ve even had to drain wine/vinegar from a gas tank. Accidents happen, especially when gas refill cans aren’t clearly marked.

If you suspect gas contamination, you’ll need to drain the tank, carburetor bowl, and fit a new inline filter.

4 Condensation

Those from a warmer climate may not be familiar with white smoke at startup. It’s part of motoring life in colder climates. The exhaust pipe gases create condensation as it meets the cold ambient air. As the engine warms up, the white smoke increases in opacity and reduces in quantity.

If this sounds like your symptom, you’ve got nothing to worry about.

Other Possible Causes

Here’s a list of other possible causes of white smoke in a four-stroke motor, some are serious, and some and relatively easy to fix.

Oil stem valve seals – These oil seals live at the top of the engine on the valve stem. They allow for cylinder head lubrication, however, when they age they become brittle and allow oil to sneak into the engine, especially noticeable by increased smoke on initial startup.

Cylinder head gasket – graphite material between the engine block and cylinder head. Its job is to seal the combustion chamber and help keep crankcase oil separate from the combustion chamber.

Worn cylinder rings – Worn rings are possible too. This does require an engine strip down to fix and while in there it usually makes sense to take care of a few other jobs like vale reseating, oil stem vale seals, head gasket, etc.

A leak-down test is excellent at detecting a cylinder compression issue.

You’ll find the tools I recommend including head gasket test kit here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.

You may find these posts useful:

ATV coolant in the cylinder

ATV coolant in the oil

How to tell ATV jumped time?

ATV spark plug black

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post Air Cooled ATV White Smoke (This will fix it!) appeared first on ATVFixed.com.

Spark arrestors on some bikes can look pretty cool, but more importantly, they serve a very useful function.

All internal combustion engines operated in the USA must have spark arrestors fitted, including four-stroke engines.

In this post, you’ll learn what a spark arrestor does, where you must use it, and why some don’t like using them.

Spark Arrestor

Spark arrestors are needed on all internal combustion equipment, two strokes or four strokes. It is fair to say that two-strokes are more commonly associated with sparks from the tailpipe.

That’s because two strokes rev at a much higher rpm and the gas oil mix tends to soot up and gather inside the muffler. As the tailpipe gets hotter, the soot catches fire, and if not for the spark arresting screen inside the exhaust tailpipe, the embers may be blown out of the tailpipe possibly causing a forest fire.

The USDA spark arrester guide specifies that all internal combustion machinery must comply with forest services spec 5100-1d – they must have a working spark arrestor. While USDA states you need a spark arrester to ride on public trails, it is permissible to operate an internal combustion engine without a spark arrester on private lands.

How to Check If You Have One?

Most kit will have one fitted from new but do check before you pull the pin. A good shop won’t have a problem fitting a spark arrestor. Modified used equipment likewise may not have them installed.

Most quality makers will have the spark arrestor part number and flow rating marked for all to see. Take a look at the very tip of the exhaust, look for model number or patient or flow rate, something like 28 cfm.

But if you don’t see a stamp, you can just check for an arrester yourself, the spark screen is easy to spot. Use your phone light to look into the tailpipe, if you see a mesh screen, you have an arrester fitted.

Can I Fit One?

Yes, you can fit a spark arrestor easily. The aftermarket suppliers will have one to suit your make and model. Most require a drill and screws or some pop rivets to secure them right onto the existing tailpipe.

Do They Effect Performance

Yes, they do. Anything that restricts either the intake of air or the exhausting of gases will affect performance. But truthfully, it’s very slight, and most won’t even notice it. What you will notice is a distinct lack of performance if you don’t maintain the spark arrestor. A two-stroke will need more attention than a four-stroke engine.

How Often Should I Clean Spark Arrester?

All engine manufacturers will have their own specified maintenance schedule for cleaning however every six months or about 150 hours of riding is normal for four-stroke engines. Two-stroke spark arresters will require more regular checking and cleaning.

Diagnosing a Blocked Spark Arrester

Spark arresters as you know, block or catch embers but they also trap carbon deposits in the very fine screen mesh which if not removed chokes the engine preventing spent gases from leaving the motor.

If spent gases can’t leave the muffler quickly it follows, the new engine cycle can’t begin, which results in poor engine performance. A fast efficient bike needs a clear airway and a clear exhaust path.

Two-strokes suffer the most, the oily gas mix of a two-stroke causes the arrestors to clog up more quickly. The arrestors block up with soot and begins to choke the engine progressively.

Symptoms of a blocked arrester vary by how badly blocked it is, typically you’ll notice:

• Hard starting
• Won’t start
• Starts then dies
• Lacks power
• Erratic running
• Won’t idle

How to check the arrester?

If it’s been six months since you last cleaned it, and or you’ve covered about 150 hours riding then you can be sure it needs cleaning.

1. Check the exhaust out put, is the exhaust pressure weak or strong?
2. Remove the screen, is it dirty?
3. Run the engine, has that improved the issue?

The screens are reusable but replace them if they’re choked or damaged or the screen is worn out. Old screens simply burn out in the center where they get hottest and see the most action.

How to Clean Spark Arrester

This is a really simple job that brings huge benefits to your engine. Removing and cleaning a clogged arrester is a five-minute task. You’ll need a Philips screwdriver (usually) and a wire brush.

The process is as follows:

• Locate the fasteners on the silencer body and remove
• Remove the arrester (metal screen)
• Use a wire brush to remove sooty carbon deposits (should be able to see through the screen when clean)
• Refit the arrester (add some copper grease to the arrester screws)

Replace a broken arrester, otherwise, it isn’t an arrester.

Job done!

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page and on the Dirt bike parts page.

You may find the following posts helpful:

How often should I service my ATV?

Do ATVs have titles?

How often should I start my ATV?

How to start ATV in cold weather?

Should you dirt bike alone?

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post Do Four Strokes need Spark Arrestor? (Yes, here’s why) appeared first on ATVFixed.com.

A little choke helps your engine start from cold. Some bikes seem to run better with the choke on permanently. But that’s your bike’s way of telling you it has a problem.

The top 5 reasons you shouldn’t ride with your choke on include:

1. Engine runs rich
2. Dilutes oil
3. Washes the cylinder
4. Burns valves
5. Causes backfiring

In this post, you’ll learn why you shouldn’t ride with the choke on, what it means if your engine runs better with it on permanently, and what you need to do to fix it.

1 Engine Runs Rich

Your carburetor’s job is to mix gas and air together to a precise ratio of 14.7 parts oxygen to 1 part gas. This is the ideal ratio. It’s the mix that produces the most power and burns more completely. It’s known as stoichiometric. Changing this recipe changes how your engine performs and how your bike handles the gas.

Your choke lever, as you know, causes extra gas to enter the engine, and that’s great for a cold engine. That’s because cold air contains more oxygen than warm air, extra gas (choke) is needed to start a cold engine. It brings the ratio closer to stoichiometric.

As the engine warms, oxygen levels normalize, and if the choke is still on, your engine is now getting too much gas and is described as running rich. A rich engine, apart from not running at its best, can have some adverse effects on your engine. Some of them can be serious and we cover them in a little more detail below.

Symptoms of a rich running engine include:

• Misfiring
• Black smoke
• Spark plug fouling
• Black sooty spark plug

2 Dilutes Oil

A rich running engine has a hard time burning all the gas. Instead, some of the excess gas makes its way to the crankcase, where it dilutes the oil. Diluted oil is thinner and won’t coat, cool, and protect internal engine components like fresh oil. There is a real danger of engine seizure when riding with diluted oil.

Contaminated oil will look thin, watery, and stink of gas. In addition, you notice your oil level higher than normal

3 Washes The Cylinder

Un-burnt gas inside the combustion chamber, as you know, makes its way to the crankcase, but to get there, it must slip past the piston and rings. As it does, it washes the protective oil coating from the wall of the cylinder. The rings make direct contact with the wall of the cylinder and need the oil coat to lubricate and cool.

A washed cylinder will cause the rings to wear prematurely and possible cylinder damage too.

4 Burnt Valves

Your engine’s valves open to allow fuel in and spent gases out. When closed, they create a tight seal. Extra gas that hasn’t been burnt and hasn’t slipped past the rings to the crankcase gets expelled out the exhaust valve. The constant washing of gas past the valve and seat causes the face to erode.

A worn valve face doesn’t create a good seal, and engine compression drops. The only fix here is to replace the valves.

5 Causes Backfiring

Backfiring is a loud bang from the exhaust of your bike. It’s caused by the un-burnt extra gas in the cylinder, which is pushed out the exhaust valve (as mentioned) and then ignited by the hot manifold or exhaust pipe.

Consistent backfiring can cause damage to your motor. Explosions are designed to occur inside the combustion chamber.

Valve and exhaust damage is usual if the root cause isn’t fixed.

Engine Won’t Run Without Choke

An engine that will only run if the choke is partially on is a very common issue. It means your engine is running lean (lacks gas), and as you’ve learned, applying the choke adds gas and that’s why it runs better with coke on. The problem is, it’s an imprecise solution and although, your bike needs the extra gas, adding choke will likely at times add too much which as you already know causes other problems.

The root cause of the issue is most likely your carburetor, it’s likely partially blocked. Your carburetor isn’t hugely complex but is a precision instrument.

Even a little grit can block important fuel passages or orifices. Your carburetor employs brass hollowed-out screws with very precise holes to add just the right amount of gas for a given throttle demand. These hollowed out screws are known as fuel jets.

As the jet holes are tiny, they block easily. Your bike will likely have two jets, maybe more. Each jet is responsible for different fuel circuits.

1. The Pilot jet is responsible for idle to 1/4 throttle circuit.
2. Needle jet is responsible for 1/4 to 3/4 throttle circuit.
3. Main jet is responsiple for 3/4 to full throttle circuit.

If your bike won’t idle, it’s likely the pilot (aka idle) circuit that’s causing the problem. The most common cause is a plugged-up pilot jet. Removing the pilot jet and cleaning will fix the issue.

To remove the pilot, you’ll need to remove the carburetor fuel bowl and remove the pilot jet. Some carburetors are a pain in the ass to access, but some can be rotated enough to gain access.

The jet unscrews, but use a good fit screwdriver. Jets are made from brass which is a really sodft metal and easily damaged. Use a strand of fine wire (strip some electrical cable for fine wire), and probe the jet. Don’t be tempted to bore the holes bigger, that will cause you no end of problems.

The main jet lives right beside the pilot and could likely do with some love too. As an alternative, go ahead and take the carburetor off the bike, strip the carb and clean it in an ultrasonic tank. It’s worth the extra effort and you’ll notice a big lift in performance.

You may find the following posts useful:

ATV dies when choke off

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• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post Can I Ride With Choke On? (5 Reasons you shouldn’t) appeared first on ATVFixed.com.

Smelling raw gas from your ATV can be alarming, especially if you park it in the garage hot.

A smell of gas from ATV oil is commonly caused by:

1. Leaking carburetor valve needle or seat
2. Incorrect fuel float setting
3. Faulty petcock

In this post, you’ll learn why your ATV oil smells like gas, how you can diagnose the problem, and how you can fix it. We’ll also cover the dangers of contaminated crankcase oil.

1 Leaking Carburetor Float Valve

Your ATV carburetor is a multi-tasking precision piece of kit. It’s got three main jobs:

1. Mix air and gas and to a precise ratio
2. Supply the correct quantity for any given engine load
3. Keep a sufficient quantity in the fuel bowl at all times

When I smell raw gas from engine oil, I immediately suspect a possible problem with the carburetor float needle. A common symptom is, as you know, the smell of gas but also an unusually high oil level and possibly gas inside the air-box.

Your carburetor is fitted with a fuel bowl. It’s a reserve of gas that stands ready to supply the engine. The gas level in the bowl is controlled by the float, float needle, and seat.

The needle and seat block a fuel passage, and attached to the needle is the float which rises and falls with the gas level inside the bowl.

As the float falls, the needle unseats, and gas fills the bowl. As the gas level rises, the needle is once again seated, and the gas flow stops. A rubber seal is used either on the tip of the needle or in the seat. As the needle gets older, it perishes and splits, as you can imagine allowing gas to seep into the bowl.

The gas fills the carburetor and very often overflows into the cylinder through an open intake valve. Gravity forces the gas inside the cylinder to leak past the rings and make its way to the crankcase.

Hydro-locking is also common when bikes get stuck in water, but gas can also cause hydro-locking. When gas fills the cylinder, it can’t be compressed, so the piston won’t move.

Hitting the start button offers a click of the starter and nothing else. The rider understandably assumes it’s a flat battery.

Checking the Needle

A leaking needle and seat are so common that if you own your bike long enough, it will happen. To confirm a leaking needle, remove the fuel bowl. Some bikes won’t make this easy. You may need to remove the whole carburetor.

With the bowl removed and a fuel line connected, lift the float. Fuel should stop flowing. Examine the needle seal. It may be on the tip or in the seat.

If your carb model has a needle and seat, go ahead and replace both, nobody likes visiting the same job twice.

2 Fuel Float

The fuel float lives inside the bowl and controls the fuel bowl fuel level. If the float isn’t set correctly, it may overfill the bowl, which will have the same effect as a leaking needle. Setting the bowl will require removing the fuel bowl and possibly the carburetor. The float may have a metal or plastic tang, the metal is adjustable, but the plastic isn’t.

To adjust the metal tang, first, you’ll find your carb float specs. Then you’ll need to measure float travel and adjust the metal tang by simply bending it and rechecking.

A worn float with a plastic tang will need to be replaced as it can’t be adjusted.

3 Petcock Faulty

A petcock or fuel valve is fitted to your fuel line. Two types are common, the manual type and the vacuum-operated auto type. The vacuum-operated type employs a rubber diaphragm and a vacuum line from the carburetor. As the engine cranks, the engine vacuum pulls on the diaphragm and actuates the valve.

Problems with older diaphragms can occur and may allow gas to leak past the diaphragm and into the combustion chamber. Your engine will run extremely rich. You may notice black smoke, backfiring, and bogging. A rich running engine will cause misfiring, and that means un-burnt gas will make its way to the crankcase.

To check the petcock, remove the vacuum line. Gas in the line spells a failed diaphragm. You can also bypass the valve and block the vacuum line for testing.

Dangers of Contaminated Oil

The dangers associated with a rich running ATV engine are real, gas in the oil dilutes it, and that means your internal engine components aren’t lubed or cooled correctly. In addition, raw gas washing down the cylinder removes the protective oil coating. This means premature engine wear or total failure.

A rich running engine will also allow a build-up of contaminants inside the cylinder head, leading to overheating, pre-ignition, burnt valves, and seats. After you find and fix the cause of your leak, it’s very important to change your oil, oil filter, spark plug, and clean the air filter.

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.

You may find the following posts helpful:

ATV car leaking gas

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• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post ATV Oil Smells Like Gas (Fixed) appeared first on ATVFixed.com.

Aragh, I know the feeling. There’s never a good time for a mechanical fault. Not to worry, we’ll get it figured out.

The top 4 reasons an ATV dies when you give it gas:

1. Not enough gas (clogged main jet)
2. Too much gas
3. Ignition fault
4. Plugged muffler

In this post, you’ll learn about the most likely causes of a stalling ATV and what you can do to fix them.

In my experience, three common faults cause this condition: dirty main fuel jet, incorrect fuel mix setting, and incorrect needle clip position. We’ll cover all of these in this post and other possibilities too.

Fuel System Overview

Most stalling issues are caused by a fueling issue, either too little or too much. Before we get into the details of your problem, it may be helpful to outline how an ATV fuel system works and the fuel ratio it likes.

You may find this post useful also – ATV fuel filter not filling up

Fuel-injected fuel systems – Some modern ATVs employ fuel-injected ECU-controlled fuel systems. This guide doesn’t cover those types of models. If you have a fuel-injected type system, begin your diagnosis by reading DTC’S. (Diagnostic Trouble Codes).

When you give it gas, a common cause of a fuel-injected engine stall is a throttle position sensor fault and fuel injector issue.

Check the wiring terminals are secure and undamaged.

Fuel-injected bikes store fault codes and so that’s the smartest place to begin diagnosis.

Carburetor fuel systems – As most ATVs run carburetor-type fuel systems, this guide will cover those.

Your ATV carburetor is a precise piece of kit and is tasked with three distinct jobs.

1. Mix air and gas together to a precise ratio
2. Supply the correct quantity for the given engine load
3. Hold a sufficient store of gas in reserve

Gas engines like to run with an air-fuel ratio (AFR) of 14.7 parts air to one part gas. This is the optimum ratio and is known as “Stoichiometric.” When a technician tunes your carburetor, this is the ratio they are chasing.

As you’ll learn, lots of things affect the AFR, most can be controlled by the rider, but some can’t.

Diagnosing

In most cases cleaning the main jet will fix your problem; that said, it won’t hurt to run a few quick tests first to help confirm our suspicions.

Question 1:

Does your condition improve if you apply the choke lever? If it does, you have a lean condition. See adjusting your carburetor below.

Question 2:

Does removing the air filter help? If it does, your engine is running rich. See adjusting carburetor below.

Question 3:

Does the engine only die if you open the throttle quickly? If it does, your accelerator pump may need attention. See adjusting the accelerator pump below.

Question 4:

Does your engine die if you open the throttle both quickly and slowly? If it does, your main jet may be clogged. You’ll need to remove and clean your carburetor.

Question 5:

What’s the spark plug condition? A black plug indicates a rich running engine, and a grey/white plug indicates a lean condition.

Question 6:

Have you made any mods like a bigger air filter or exhaust or a change in altitude or temperature? These types of changes will require a fuel adjustment and possibly a re-jetting of the carburetor.

All diagnoses should begin with fresh gas in the tank and a clean air filter. You should also know that clogged carburetor jets cause the most running issues. It never hurts to remove and clean your carburetor thoroughly.

The answers to the above questions will put you on the correct path.

Running Lean

When your engine isn’t receiving enough gas in proportion to air, it’s known as running lean. Or another way to look at this situation – the engine is getting too much air.

Symptoms of a lean engine vary by how lean it’s running, but here are a few of the more common ones:

• Hanging idle
• Surging
• Bogging
• Stalling
• Popping
• Starts and dies
• Only runs on choke
• Dies when give it gas

The causes of a lean engine are just as varied. Here’s a list of the more common ones and the fix:

• Cold ambient temperatures or higher altitudes – adjust mix
• Mix out of adjustment – adjust mix
• Stale gas – replace with fresh gas
• Blocked carb jets – remove and clean carb
• Low bowl fuel level – adjust float
• Engine mods – mods like bigger air filters or quick flow exhausts will likely require re-jetting the carburetor
• Vacuum leak – check carb bolts are tight and carb gaskets and manifolds for leaks
• Faulty fuel pump – check fuel flow
• Valve lash out of spec – adjust

Regular maintenance and a fuel stabilizer are crucial to keep your ATV running smoothly, maintenance includes annual carb cleanouts and regular air filter cleaning/oiling. Skipping these can shorten the life of a carburetor and, in some cases, you might find your carburetor is simply at the end of the road.

In those cases, don’t hesitate to replace it. New carbs aren’t as spendy as you might imagine; check out the Amazon link below.

You may find these posts helpful:

• Why does my ATV make a popping noise?
• ATV idles up and down
• Why is my ATV bogging down?
• ATV dies when choke is off

Accelerator Pump

A very common cause of stalling when giving it gas is an accelerator pump fault. The pump is only used when you gun the throttle from idle. Its purpose is to inject a gas shot into the carburetor, which helps counteract the lean condition caused by the rush of air as you nail the throttle wide open.

How does it work? The system employs two main components:

1. Pump
2. Leak jet

The pump consists of a rubber diaphragm, fuel orifice, and adjustable cam. When activated, the throttle assembly pushes on the pump cam, causing the diaphragm to shoot gas through an orifice directed at the venturi. (Worth noting not all systems will work exactly like this, but this type is typical.)

Adjusting the point of contact between the throttle and pump cam affects the timing and duration of the gas shot. A good gas shot should last about one second and be timed to barely miss the slide as it opens.

If the gas shot hits the slide, its effectiveness is reduced. You’ll need to adjust the cam so that the shot arrives just after the slide lifts.

Although I’ve shown the AP here on a CV-type carb, it’s really only commonly found on a mechanical slide carb.

Problems with the pump include:

• Timing off
• Worn diaphragm

You can check your pump operation by removing the intake ducting operating the throttle quickly, and observing the gas shot.

The Leak jet removes gas when not needed by the pump. When the throttle is opened slowly, the gas simply passes through the leak jet and back to the carburetor bowl.

The quantity of gas supplied by the pump is directly affected by the size of the leak jet. A smaller leak jet supplies more gas to the pump, and a bigger leak jet reduces the volume of gas to the pump.

Problems with the leak jet include:

• Incorrect sizing
• Blockages

The volume of gas supplied by the accelerator pump is directly affected by timing, duration and the leak jet fitted. You can eliminate this as a possible cause by opening the throttle slowly. If the problem isn’t present, your accelerator pump needs attention. If the problem persists, try adjusting the carburetor. See below.

Running Rich

Your engine is said to be running rich (aka fat) when it’s receiving too much gas in proportion to the volume of air it’s receiving. Or another way to look at this – your engine isn’t receiving enough air.

Symptoms of a rich running engine include:

• Bogging
• Stalling
• Backfiring
• Black smoke
• Misfiring
• Wet plug
• Black plug

Common causes of a rich running engine include:

• Mix out of adjustment – adjust
• Dirty air filter – clean or replace
• Leaking float needle – replace
• High bowl float level – adjust
• Faulty petcock – replace
• Faulty carb – replace
• Incorrectly jetted carb – re-jet

You may find these posts helpful; they deal with rich running engines:

• Why is my ATV running rich?
• ATV oil smells like gas
• Why is my ATV bogging down?
• Why is my ATV spark plug black?

Adjusting Carburetor Fuel Mix

Adjusting your mix is a little technical but not brain surgery. Most ATV carburetors will have three fuel circuits.

Idle Circuit (Pilot jet)- supplies gas at light to mid-throttle stage but is solely responsible for idling. 0 to 1/4 throttle

Midrange Circuit (Needle jet) – supplies gas between 1/4 to 3/4 throttle

Main Circuit (Main jet) – supplies gas to needle jet circuit, from 3/4 to full throttle

A standard adjusting procedure looks like this –

Step 1

Begin with a warm engine. Check how the throttle responds throughout the range. Turn the engine off, find your base setting by turning the pilot circuit screw (mix screw) all the way home (clockwise) until it seats, count the number of turns. (1.5 to 2 is normal).

Return the screw to its original setting.

Step 2

Start the engine and turn the mix screw clockwise until the engine stalls. (note the amount turned and return after stall)

Step 3

Restart the engine, now turn the screw anti-clockwise until the engine stalls.

Step 4

Restart the engine and turn the mix screw clockwise until the engine rpm is at its highest.

Step 5

Now reduce the idle screw to where the idle is smooth, anywhere from 1000 – 1500 rpm.

If, after this procedure, your mix screw is set to more than 2 turns out or less than one turn out, it’s a strong indication your carburetor needs re-jetting.

Your mix screw is now set correctly. The throttle should respond sharply and without hesitation or bog.

If it does bog, your:

• Needle clip position may need adjusting
• Carburetor main jet is dirty
• Carburetor needs re-jetting

Needle Clip Position

Your needle lives in the heart of your carburetor, and to access it, you’ll need to remove it from the bike. The needle moves up and down inside the emulsion tube in response to throttle application. The higher the needle inside the emulsion tube, the more gas the engine gets.

A clip at the top of the needle sets the base height of the needle; it has five positions. The clip is usually set to the 3rd position down. Moving the clip down one position will hold the needle higher up and help supply more gas (Richer). Conversely, moving the clip up will lean out the mix.

Adjusting the clip position is a trial-and-error procedure. A systematic approach works best, as removing and fitting some carbs can be a pain in the ass.

Ignition Fault

An ignition fault can allow a bike to idle fine but fail at higher rpm. If you’d like to read more about ATV ignition systems, check out ATV Ignition system.

Here are some links to simple checks you can make. Note some bikes will run without a battery, while others require a strong, fully charged battery. Use a voltmeter and check your battery as per the following links:

• ATV battery test
• ATV loose battery terminals
• ATV dirty battery terminals

Check also that the battery is charging at idle – Anything over 12.65 indicates it’s charging.

A faulty spark plug or the wrong plug type is a common cause of intermittent performance issues. Best to confirm the plug code by checking your owner’s manual.

Check the spark plug condition and read the color – Check the ATV Plug color guide for what each color means.

Check out ATV spark plug link for some more detail on the importance of a known-good spark plug when troubleshooting.

Visually check the condition of your plug cap, plug wire, and coil.

Using a simple in-line spark tester, fit the tester and check the spark as you give the bike gas.

If the spark in the inspection window fails, you’ll need to check the resistor cap and run a resistance test on the coil, stator, and pickup; also possible for the CDI box to cause a stalling issue.

You may find these links helpful:

• Coil and cap test
• Stator test
• Pick-up test
• CDI box fault

You’ll find the tools I recommend, including an inline ignition system test, here on the ATV tools page, and you’ll find common spare parts here on the ATV parts page.

Plugged Exhaust

This isn’t a hugely common cause of stalling, but it does happen. The spark arrester inside the exhaust becomes caked in soot, so thick that exhaust gases can’t get out, and it causes the engine to stall at anything above idle.

With the engine idling, hold a shop towel firmly over the tailpipe using a gloved hand. Release it after 3-4 seconds. The pressure built up should be great. If it’s weak, it suggests a partial blockage.

For more details on diagnosing, check out this post – Do ATVs need spark arrester?

Go ahead and remove your spark arrester and clean it.

Check out this link for a cleaning guide – Spark arrester cleaning

A comprehensive ATV no-start guide that will get you rolling in jig time.

ATV no-start guide

You may find the following posts helpful:

• Why is ATV bogging down?
• Can I ride with choke on?
• ATV oil smells like gas

I’ve written a ton of ATV troubleshooting posts. Hopefully, you won’t need them, but if you do, we have you covered.

ATV Troubleshooting Guides

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

• ATV Rear Brake Pedal Stuck - Solved!
• How to Tell ATV Fuel Pump is Bad? This is how ...
• Will Dirt Bike Start If Timing Off? Run this test

The post ATV Dies When Give It Gas (Check these first) appeared first on ATVFixed.com.

Riding an ATV on difficult terrain and balancing the throttle to prevent it from stalling can be quite the challenge.

The top 5 most common reasons an ATV only runs with the throttle include:

1 Idle speed needs adjusting
2 Air fuel ratio needs adjusting
3 Dirty pilot jet
4 Petcock faulty
4 Air filter dirty
5 Bad gas

In this post, you’ll learn about all the most common reasons your ATV won’t idle without throttle and what you need to do to fix it.

1 Idle Speed

Because ATVs run on rough terrain, it’s understandable if things drop out of adjustment from time to time. Your idle speed adjustment assembly holds the throttle open slightly at idle, which prevents the engine from stalling.

Try adjusting the idle screw (if applicable) or google your particular model for the location of your ATVs adjuster.

The idle adjuster doesn’t affect the fuelling ratio but should be eliminated as the possible cause before proceeding with any fuel ratio adjustments.

2 Air Fuel Ratio

Your bike needs an exact ratio of air to the fuel of 14.7:1. Although the mix is set from the factory, it doesn’t remain set for life. Wear and tear, adding mods like big air filters or fast flow exhausts will upset this mission-critical ratio.

Luckily your carburetor has a fuel mix screw. After every service, a technician will check how the bike is running and adjust the mix if necessary. Adjusting your mix is a little technical but not brain surgery. Most ATV carburetors will have three fuel circuits.

• Pilot – responsible for idling to 1/4 throttle
• Needle – responsible for 1/4 to 3/4 throttle
• Main – responsible for 3/4 to full throttle

Adjusting the air-fuel screw feeds more or less gas through the Pilot circuit. A standard adjusting procedure looks like this –

Step 1

• First, warm the engine and examine how the throttle responds throughout the range.

Step 2

• Turn the engine off, find your base setting by turning the pilot screw (mix screw) all the way home (clockwise) until it seats, counting the number of turns (about two is normal).
• Return the screw to its original setting.

Step 3

• Start the engine and have a helper balance the throttle while you turn the mix screw anti-clockwise until the engine runs by itself.
• Keep turning until it stumbles and stalls.
• Restart, idle the engine and turn the screw (clockwise this time) until it stumbles and stalls.

Step 4

• Within that window of both stalls, set the screw where the revs are at their highest.
• Now reduce the idle screw (not air-fuel mix screw) to where the engine idle is smooth, anywhere from 1000- 1500 rpm.

3 Dirty Jet

Your Pilot Jet is responsible for supplying the gas at idle. Any blockage here, and you’ll have difficulty idling. Old gas blocking up the pilot jet is a common problem, and the only fix is to remove the jet and clean it. Removing the carburetor is likely the best approach.

Gumming of the carburetor, caused by stale gas is a real problem suffered by all small engines.

Some carbs are easier than others. In some cases, it may be possible to remove just the bowl and remove the pilot jet.

4 Bad Gas

Ethanol gas is a blended gas that is quite common now. Trouble is under certain conditions gas begins to turn stale after just one month, regular gas after three. Stale gas loses its punch, but worse than that. The gas turns to a sticky, gummy sludge in the bowl of your carburetor, and that’s where your pilot and main jet live.

When this crap gets into the tiny orifices of the jet and emulsion tube, your engine either won’t run or just won’t run right. Using a fuel stabilizer will help you sidestep this kind of trouble.

If you’re storing your bike for more than a month, mix some stabilizer into the gas tank and run the engine to get the mixed gas into the carb.

You’ll be trouble-free starting the next time you hit the button.

5 Petcock

Faulty vacuum-actuated fuel valves have been known to cause fuel flow problems. The valves employ a simple diaphragm and engine vacuum hose to open the valve and allow fuel to flow. The petcock diaphragm gets old and hard and loses its will to live. It simply doesn’t open all the way, which causes a shortage of gas.

To eliminate this as a possible problem, bypass the fuel valve and go direct to the carburetor. If this solves your issue, replace it with an OEM or a standard valve and seal off the vacuum hose.

But you’ll need to remember to turn your gas off.

Other Possible Causes

A dirty air filter will generally cause a rich condition, symptoms include:

• Stalling
• Bogging
• Black smoke
• Black plug

Checking your air filter is an easy job, and most won’t require any tools. Try removing your air filter, run the engine and see if that helps.

If it does, try cleaning your air filter and using the recommended air filter oil.

If, after reinstalling the filter, the problem persists, your bike is running rich at idle and needs to be leaned out.

You may find the following posts useful:

Can I ride ATV with a choke on?

Why is my ATV bogging down?

ATV carb leaking

Can I use WD40 on my air filter?

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

• ATV Rear Brake Pedal Stuck - Solved!
• How to Tell ATV Fuel Pump is Bad? This is how ...
• Will Dirt Bike Start If Timing Off? Run this test

The post ATV Only Runs With Throttle (Top 5 causes) appeared first on ATVFixed.com.

Popping and banging noises from your ATV is annoying, but it’s also a warning sign that you probably shouldn’t ignore.

An ATV makes a popping noise because the engine is running lean, and the top 8 reasons an ATV engine runs lean include:

1. Temperatures, altitude and humidity changes
2. Carburetor out of adjustment
3. Engine modification
4. Carburetor fault
5. Bad gas
6. Vacuum leak
7. Valve lash off
8. Mechanical issue

In this post, you’ll learn what a lean condition is, why your ATV makes a popping noise and what you can do to fix it. The following post assumes your bike is fitted with a carburetor and not fuel injected.

Symptoms of Lean Engine

Lean running engine symptoms vary by engine and by modifications, but the usual telltale signs include:

• Popping
• White plug
• Hot running engine
• Misfiring
• Hanging idle
• Rough running
• Bogs on takeoff

What’s Lean Running?

A popping sound in the engine is a classic symptom of a lean running engine. Owning an ATV, you’ll be aware no doubt of the delicate balance of air to fuel (known as AFR – Air Fuel Ratio) that must be maintained by your carburetor.

Any change to how your motor breaths will have a direct effect on this balance. A ratio of 14.7 parts air (oxygen) to 1 part gas is the sweet spot for an ATV engine and is known as stoichiometric. A lean engine is a cylinder that isn’t getting enough fuel in relation to the volume of air it receives. Or another way to look at it is “engine is receiving too much air.”

A lean condition is an engine with an AFR above 14.7:1. (stoichiometric) A rich (fat) running engine is an engine that is receiving too much gas for the volume of air it’s receiving. Or another way to look at it – “engine isn’t receiving enough air.”

A rich condition is an engine with an AFR below 14.7:1. (stoichiometric)

Your carburetor is designed to measure and mix gas in the ballpark of the stoichiometric ratio. It does so using fuel jets with very precise orifices through which gas flows. Adjusting screw(s) on the body of the carburetor helps a technician fine-tune the mix. A single air-fuel mix screw is the norm, but some carburetors may have a separate screw for both (one for air and one for gas). See adjusting below.

Dangers of a Lean Condition

A lean engine runs hotter than normal, and that can lead to all sorts of expensive repairs. The lean condition, as you know, could be caused by something simple, but it could also be a symptom of a more serious underlying fault.

1 Temperature

Air temperature, altitude, and humidity all affect the volume of oxygen in the air. Colder air, for example, causes an engine to run lean because the air is denser.

At colder temperatures, the engine is sucking in a larger volume of oxygen-heavy air than at higher temperatures.

Oxygen and gas (AFR) must be mixed to stoichiometric, and unlike a car, most ATVs don’t have a closed-loop computer making real-time adjustments for oxygen volume.

Instead, we make small adjustments to the air-fuel mix screw manually and or move the carburetor clip position and in some cases, a carburetor may need a re-jet.

2 Carburetor Adjustment

Carburetors are set from the factory, but component wear, vibrations, rough terrain can all cause carburetors to fall out of adjustment. Most carburetors are fitted with one fuel mix screw. Some may have two adjustments screws – an air screw and a fuel screw.

If fitted, the air mix screw will be on the air filter side of the carburetor, and the fuel mix screw will be on the engine side of the carburetor. Adjusting the fuel mix screw anti-clockwise adds more fuel to the mix, and turning it clockwise removes gas from the mix. A normal setting for the fuel mix screw is about 1.5 – 2 turns.

An airscrew works in the opposite way. Turning anti-clockwise removes air from the mix, and turning clockwise adds air to the mix.

Below we’ll adjust a carburetor with a fuel mix screw only, often referred to as the pilot mix screw. Begin with a warm engine and find your base setting. Having a good screwdriver as pilot mix screws are made from brass, which is a soft metal and will break if abused.

Step 1

• To find your base setting, engine off, and using a screwdriver, count accurately the number of turns clockwise to seat the mix screw. No need to tighten the screw. Just seat it. A ballpark is usually about two turns

• Now, go ahead and set your mix screw back where it was. Knowing your base setting means you can return to it at any time if everything turns to crap.

Step 2

• As we believe your engine is running lean, you’ll need to move the mix screw anti-clockwise until the engine bogs and stalls. Move about 1/8 of a turn at once and test. Small changes are better as it’s easy to overdo it.

Step 3

• Move the screw clockwise now until the engine bogs and stalls.

Step 4

• Now set the screw where the revs are highest within that window. The bike should rev cleanly without bogging.

Step 5

• Now set the idle screw so that the engine idles smoothly at about 1000 rpm.

Black smoke or a black fouled spark plug indicates a rich running engine and means you’ve gone too far. If it takes more than 2 and 1/2 turns to dial in your engine, it suggests you may need to re-jet. Just under two turns is about right for a fuel mix screw. The bike should rev cleanly without bogging.

3 Modification

If you’ve had some light modification like fitting a bigger air filter or free-flow exhaust, you’ll need to adjust the carburetor. If you’ve done a re-bore or sometimes just resetting valve lash throws the cab out a hair.

Mods that help your engine suck in more air or breath more freely are great for power, but you’ll need to add more fuel to keep the ratio at that sweet spot.

Try adjusting the fuel mix, but if that doesn’t work, you’ll need to go balls deep, move a clip, or re-jet.

Re-jetting

OK, but what’s a jet? It’s a brass screw with an orifice that is very precisely measured. Each jet is marked with a number indicating the orifice size. The bigger the orifice, the more fuel the jet can supply the engine. If you’ve tried adjusting your fuel mix screw and your more than 2 and 1/2 turn out, it’s likely you need to re-jet. Re jetting your carb isn’t technical. It’s more trial and error and plug reading.

To successfully re-jet, you’ll first need to carefully assess how your carburetor is fueling at the different stages of the throttle. You’ll need to pull your carb apart and see what size pilot, main and clip position you’re running.

Most ATV carburetors are either mechanical slide or vacuum-actuated CV (constant velocity) type. These carbs usually have three main fueling circuits. Idle, Midrange and Main.

1 Idle circuit (Pilot jet) – affects idling to 1/4 throttle

2 Midrange circuit (Clip position) – controls 1/4 to 3/4 throttle

3 Main circuit (Main jet) – controls 3/4 to full throttle

In addition to these circuits, your carburetor may have an accelerator pump. It squirts a shot of gas into the venturi of the carb, but only when you nail the throttle from idle.

The pump squirt lasts about one second and is timed to miss the slide face (adjustable) as it opens.

It’s only needed when you nail the throttle as the WOT (Wide Open Throttle) causes an instant lean condition.

When not needed (gentle throttle application), the gas in this circuit is leaked back to the gas bowl using a leak jet. The leak jet is sized to allow more or less fuel leak back, which directly affects squirt volume and duration. The leak jet on your ATV may also need to be re-sized.

4 Carburetor Fault

Carburetors are precision bits of kit, not unlike a musical instrument. If it’s even slightly off-tune, you’ll know about it. A dirty carburetor is a very common cause of a lean running engine. The jets inside the carburetor may become dirty and prevent a full flow of gas to the engine.

Carb gumming has become a real problem with small engines that lay idle for a few months. Blended gas like ethanol under certain conditions starts to go stale after just one month, and left in the carb can turn into a congealed mess.

The best way to avoid this problem – use a gas stabilizer. It’s an additive for the gas that will keep it fresh for at least 12 months.

I advise using it in all your small engines, including two-stroke chainsaws, etc. It protects the whole fuel system from gumming, moisture, and corrosion. You’ll find the stabilizer I recommend here on the ATV parts page.

It never hurts to clean your carburetor and should be done at least once per year. You’ll need to remove it from the engine and strip it completely. You can use carb cleaner, or I prefer an ultrasonic tank. It won’t damage any plastic or rubber components. When rebuilding, treat her to a new gas filter too.

You could find after cleaning that your problem persists, and that’s possible. A carburetor fault, unlike a flat wheel, isn’t very obvious to the eye. So if you’ve cleaned it, adjusted it, your gas is fresh, and you can’t dial it in, go ahead and change it out.

5 Bad Gas

Old gas is losing its zing and can cause your engine to misfire and run lean.

And as you know ethanol-blended gas older than one month may already be in the process of turning stale.

If you suspect your gas is a little off, go ahead and drain it, or if less than a half tank, top it up with fresh and ride on. I use my ATV all through the summer and only use a gas stabilizer at the end of the season. I use it in all my small engine kit, riding mower, saws, generator, dirt bike, old cars, and my ATVs.

You could use it all year round, and you should if you’re only occasionally using your ATV. Old gas turns to a sticky, gummy mess inside a standing fuel system and is a carburetor killer.

Faulty Petcock

A petcock or fuel valve is fitted to all bikes, most are a simple mechanical tap, but some are vacuum operated. As the engine is cranked, a vacuum is applied to the valve, which, when all is going well opens wide and allows gas to flow freely to the carb.

If as you’ve guessed the vacuum hose to the valve leaks, the effects on the engine are twofold, firstly the hose leak leans out the mix, and secondly because of the leak the valve doesn’t open fully, causing fuel starvation which serves to further the lean condition.

You can eliminate this as a possible cause by simply bypassing the valve and testing the bike. If you find it’s failed, you can replace it with an OEM or fit a basic mechanical tap, but you will need to cap the vacuum pipe and remember to turn off your gas.

6 Vacuum Leak

What’s a vacuum leak? It’s an air leak, on the engine side of the carburetor. Loose carb bolts or a weak interface gasket or manifold is enough to cause a vacuum leak. A leak on the engine side of the carburetor will cause a lean condition and most likely an erratic idle.

Finding a vacuum leak can be a right pain in the ass, but a can of WD 40 helps. With the engine idling, try systematically spraying around the gaskets, manifold, carb adjustment screw. The WD helps seal the leak temporally, and your ear will pick up the change in how the engine sounds.

7 Valve Lash

What’s valve lash? Valves, as you know, open and close sequentially to allow air/gas mix in and spent gases out. The timing is mission-critical and is driven by a camshaft which is, in turn, driven by the crankshaft.

So what’s the problem? Rockers are employed to push on the valve tip to open it at the appropriate time and hold it open for the correct duration.

The gap between the valve tip and rocker is important, and changes as an engine naturally wears. They’re adjustable and should be as part of scheduled maintenance but are often skipped as some are a pain in the ass to access.

If the lash isn’t adjusted to spec, you can get all kinds of symptoms, depending on if the valves are too tight or too loose.

8 Mechanical Issue

A lean condition caused by a mechanical issue is usually more serious. It can mean a damaged valve or valve seat, blown head gasket, excessive blow-by.

Running a few simple tests like a leakdown test will rule this out.

You may find the following posts helpful:

Other Possible Causes

Float Tang needs adjustment

Faulty carburetor valve

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.

You may find the following posts helpful:

How to tell if ATV jumped time?

Air-cooled ATV white smoke

Why is two-stroke overheating?

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

• ATV Rear Brake Pedal Stuck - Solved!
• How to Tell ATV Fuel Pump is Bad? This is how ...
• Will Dirt Bike Start If Timing Off? Run this test

The post Why Does ATV Make Popping Noise? (This is why) appeared first on ATVFixed.com.

A smoking engine generally isn’t a good sign but let’s not meet trouble halfway.

Hard or worn valve stem oil seals will cause an ATV to smoke when first started. Replacing the valve stem seals will stop the smoking.

In this post, you’ll learn why your ATV engine smokes and what you can do to fix it.

Oil (valve) Stem Seals

Almost all ATV engines are four-stroke with an overhead valve configuration. The valves, as you know, open and close in sequence and slide inside valve guides.

The valve stem, spring, and rocker are hard-working moving parts and require oil to lubricate and cool them. Although clearance between valve stem and guide is snug, oil could easily pass from the cylinder head to the combustion chamber by seeping in between the valve and guide.

The solution to this problem is a small nylon seal engineered to slip over the valve stem and seat on top of the guide.

The seal prevents oil transfer while keeping valve stems lubed and allowing for movement. Like all components, these guys only work for so long.

Ten years is about the life span and shorter if oil changing is neglected.

So Whats The Problem?

Oil stem valve seal is an unassuming piece of kit, and it’s pretty impressive how something so small can be that durable. As the seal ages, constant heating/cooling cycles and oil contaminates make them hard. The hard seals allow oil to slip past, down the guide, and into the cylinder.

But why does it only smoke on startups? The hards worn-out seals allow a small amount of oil into the cylinder constantly, but because it is a small amount of oil, you won’t notice any smoke. Different story when you let the engine rest for a few hours.

The oil continues to leak in after shut down, but instead of burning, it rests behind the intake valve or inside the cylinder. When you start your engine from cold, the oil is burnt off immediately with the gas mix resulting in a plume of blue smoke.

What’s The Solution

Some have tried an oil conditioner that promises to recondition the seals, and while I’ve seen some success with this, my inner mechanic would never run for this solution. The correct fix is to remove the cylinder head and replace the valve stems seals.

While the head is off, you could de-carbon, re-seat, and adjust valve lash on reassembly. A new head-gasket will be needed too.

It is possible to replace the seals without removing the cylinder head if you have room to work. To attempt this, you’ll need a special spring compressor kit and some clean new nylon rope. Filling the cylinder with rope and moving the piston up to meet the cylinder head prevents the valve from falling into the cylinder. It can be tedious to accomplish but does work.

Worn Valve Guides

The valves as you know slide inside sleeves known as valve guides with the seal sitting over the top preventing oil ingress. Problems arise as valve guides wear and allow for greater free play between guide and valve. The increased free play stretches the seal and damages it-which allows oil to leak into the cylinder.

Replacing the seals won’t fix the problem, the valve guides will need to be replaced and that requires removing the cylinder head.

Other Possible Causes

While a valve seal is the most common cause for smoke on start it isn’t the only possible cause. Here’s a list of a few others worth checking out:

Oil quantity – Too little oil is bad, but so too is too much oil.

An overfull oil level will cause the engine to burn off the excess.

Oil type – Oil type is important, using an oil that’s too thin may cause it to leak past seals and rings. While a thin oil is best for super low temperatures it may not be suitable for warmer climates.

Check what your manufacturer recommends for your engine.

Carburetor issue – A leaking carburetor needle valve or incorrectly adjusted float may cause gas to flood the engine and often results in an increased oil level, and white smoke.

Common symptoms of a worn arb needle seal include:

• Stink of raw gas
• Overfull oil level
• Oil leaks
• Engine smoke

Fuel issue – Contaminated fuel, while a four-stroke engine will run on two strokes mixed gas it won’t like it much. It will cause the engine to smoke and also on startup. Worth checking if the wrong gas was used.

You may also find these posts helpful:

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• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post ATV Smokes When First Started (This is why) appeared first on ATVFixed.com.

An erratic idling ATV engine is so annoying but could point to a far more serious problem.

The four most likely causes of an ATV idling up and down include:

1. Vacuum leak
2. Bad gas
3. Fuel restriction
4. Tight Valves

In this post, you’ll learn why your ATV engine idles erratically and what you can do to fix it. Always check your spark plug condition and be sure the correct type is fitted. In addition be sure your gas is fresh. Both these errors are a common source of a wide variety of running issues.

1 Vacuum Leak

Air/fuel mix is drawn in through the carburetor under a vacuum which is created by the piston as it moves down the bore.

The air and fuel are mixed by the carburetor very precisely.

The AFR (Air Fuel Ratio) is 14.7:1 for gas engines. Any interruption of either gas flow or airflow causes the ratio to change, and that will affect how the engine performs.

Symptoms Of Erratic Idling

The classic symptoms of a vacuum leak include an erratic idle. The engine does its own thing revving up and down, but once on the move, the problem isn’t noticeable. Your spark plug may be a grey whitish color, and the engine may misfire.

What is a vacuum leak? Your carburetor is a clever bit of kit. It takes air in through the intake, where it passes over the venturi speeding up the airflow in the process and creating a vacuum that lifts gas from the fuel bowl.

The carb is designed to supply about 1 part gas for every 14.7 parts of air. Adjuster (s) on the carb allows for fine-tuning the ratio.

So what’s the problem? Air that doesn’t pass through the venturi isn’t calculated (un-metered), and that causes a lean condition inside the engine. A lean condition is a situation where there’s too much air in the mix or another way to look at it – not enough gas.

But why is the idling erratic? Erratic idling is likely caused by the erratic nature of the air leak.

Sources Of A Vacuum Leak

The most common sources of a vacuum leak include:

• Loose carburetor
• Damaged intake gaskets
• Cracked intake manifold
• Adjusting mix screw seal worn
• Faulty carburetor
• Damaged or valves out of adjustment
• Headgasket failure

Locating Vacuum Leak

Check for obvious signs of damaged gaskets or loose carburetor bolts. A can of WD40 helps seal off vacuum leaks temporally. With the engine idling, systematically spray around the carburetor to engine union and around the carb adjusting screw. When the surging stops, you find the location of the leak.

2 Old Gas

Old gas causes lots of problems in small engines. Regular gas starts to go stale under certain conditions after just one month, and old gas doesn’t have any Oomph.

Erratic idling and poor running are symptoms of old gas. This is an easy problem to solve. Just drain the old gas out and fill it with fresh gas.

A gas stabilizer additive will help keep your gas fresh for up to two years and is advisable for all small engines, especially those that sit idle for more than a month.

3 Restricted Gas Flow

A restricted gas flow will cause lean erratic running. Common causes of gas restriction include:

• Blocked idle (Pilot) jet
• Float out of adjustment
• Faulty float needle
• Restricted gas filter
• Restricted in tank

Blocked jets are common and cleaning will fix the problem.

4 Tight Valves

Your engine valves are responsible for allowing the gas mix in, and the spent gases out. The valves are opened by rockers which are driven by the crank and camshaft. The valve tip to rocker gap is known as a lash, and this gap is important.

If your intake valve lash is too tight, it may not seat. This will allow extra air into the cylinder, lean out the mix and cause erratic idling.

A tight valve will cause your engine to run hot, and as the valve isn’t closing completely, it can’t transfer heat to the cylinder head. In addition, a tight valve is liable to float, reducing power at the top end.

Checking valve lash is preventative maintenance and is often neglected. It’s a job you can easily take care of yourself, just some basic tools and an inexpensive tool called a feeler gauge.

A tight valve, if not adjusted, will burn the valve and seat.

Engine Damage

Erratic idling, in most cases, is caused by a vacuum leak, which means your engine is running lean. A lean engine runs hot, and that can spell trouble, blown head-gaskets, seized bearings, seized piston, etc.

If your valves are tight, that can result in damaged valves, valve seats, valve guides, cylinder-head damage, etc.

Other Possible Causes

Ignition timing is important. An erratic spark will cause all sorts of issues. An incorrect plug type or plug gap may cause an incomplete burn.

Check plug type and plug gap.

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.

You may find the following posts useful:

Why is my ATV bogging down?

Carburetor leaking gas

Why does ATV make popping noise?

• About the Author
• Latest Posts

John Cunningham

John Cunningham is a technical writer here at ATVfixed.com. He’s a Red Seal Qualified Service Technician with over twenty-five years experience. He’s worked on all types of mechanical equipment, from cars and trucks to ATVs and Dirt bikes.

www.atvfixed.com/about-john-cunningham/

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The post ATV Idles Up and Down (This will fix it!) appeared first on ATVFixed.com.