ATV Dies When Give It Gas (Check these first)

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 detail of your problem, it may be helpful to outline how an ATV fuel system works and the fuel ratio it likes.

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).

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

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

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.

Problems with the pump include:

• Timing off
• Worn diaphragm

You can check your pump operation by removing the intake ducting and 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.

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.

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

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.

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.

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?