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ATV Won’t Start When Cold (This is why)

I look forward to heavy snowfall, which gives me an excuse to ride the Quad, but for some, the cold weather brings disappointment.

When an ATV doesn’t start in the cold, try applying the choke lever. Other possible reasons an ATV won’t start when cold include:

  • Battery low
  • Stale gas
  • Choke needs adjustment
  • Frozen carburetor
  • Wrong engine oil type

In this post, you’ll learn about all the most likely reasons your ATV won’t start in cold weather and what you can do to fix it right now.

Check Spark Plug First!

Before going any further, save yourself a ton of time, check the spark plug is the correct type. While spark plugs look the same and fit your engine perfectly, they are different. They are categorized by size and length, but also by their heat range. A plug that is too cold for your bike will cause a ton of issues including difficult cold starts.

Spark plug

A spark plug should get hot enough so as to burn off contaminates but not so hot that’s it pre ignites. Having an incorrect spark plug fitted is really common.

Check your make and model with the manufacturer, don’t rely on the plug you have removed as a reference unless you know the engine from new.

In line ignition system tester

If you suspect a spark plug issue, run an inline spark test, and have a helper crank over the engine.

Youll find an inline spark tester here on the ATV tools page.

Cold Starting an ATV

Most ATVs will fire right up when you hit the start button, but when the temperatures get low, most engines will require an extra step in the starting procedure. The extra step is either activated by the rider manually or it’s automatically activated.

There are two types of automated activation, a basic thermostatically activated type and the more sophisticated ECU (Engine Control Module) type fitted to fuel injected engines. If your bike is fuel injected, you can jump ahead here.

Manual Choke

The choke button/lever is a manual control the operator must use to start the engine in cold temperatures. Applying the choke creates just the right air to fuel mixture to start the cold engine, and that ratio is important. If it’s off, the engine just won’t operate.

The ratio is known as AFR (Air Fuel Ratio), and the optimum ratio is fourteen point seven parts air to one part gas, written as 14.7:1. I don’t want to get too far into the weeds here, but a quick explanation of the problem is – Cold air is denser than warm air, and so cold air is oxygen-rich which throws the air-fuel ratio way off (known as a lean condition, i.e., the mix lacks sufficient gas).

The solution to the problem is as you imagine – adjust the ratio so that it’s closer to 14.7:1 and to do that, we use the manual choke lever. The choke, as its name suggests, restricts or chokes off the air supply to the engine and is manually adjustable, but for some ATVs, it’s automated (more on this below).

Auto Choke

Engines respond to ambient temperatures and so require choke proportionally and that’s why auto chokes are so convenient. An auto choke requires no in-put from the rider. Many modern ATVs employ an auto choke setup.

So, where is the choke lever located?

Your choke lever (if fitted) will be located in a convenient location on the handlebars or close to the carburetor. Two basic types are common “Plunger type,” pull to apply and push for off, usually fitted to the handlebars, and the “Lever type” usually mounted on the carburetor and are often discretely located.

If you are unfamiliar, google the location by your make and model, use the google picture search for fast visual aid.

How To Use Choke

The choke is, as you know, a very simple but effective solution to starting a cold ATV engine. To use it effectively, begin by locating the choke plunger or lever. The locations will vary from model to model but usually on the handlebars or mounted on the carburetor itself.

The carburetor is mounted on the engine, located directly below the gas tank. Carburetor-mounted choke controls can sometimes be less obvious than handle-bar-mounted controls.

You may need to dismount and take a good look at either side of the engine, but the lever will always be easily accessible. You won’t need to remove any covers, and you’ll be able to locate it next time by feeling from the seat.

ATV Choke

The choke symbol, parallel lines with a diagonal line in the middle, kind of like a capital “N” shape, is distinct and is usually marked on the control.

  • With the choke located, set it to full and crank over the engine. After the engine starts, move the choke control to halfway.
  • Most engines will be happy with 1/2 choke immediately after start, but if your engine stumbles and stalls, give it some more choke until you find the sweet spot.
  • As your engine starts to warm, you’ll find it won’t like as much choke, and so you’ll need to adjust. A fully warmed engine won’t like choke and will run poorly if the choke is on (running rich).
  • Warm-up time will be dictated by ambient temperatures, but after 2 or 3 minutes and we should be good roll. It’s never a good idea to drive with the choke on as the engine isn’t yet up to operating temperature.

Fuel Injected Cold Start

The latest kit may have a fuel-injected fuel system, if that is the case your bike relies on an ECU to make cold start fuelling decisions. A bike loves a very precise fuel ratio, it’s known as the Air to Fuel Ratio (AFR), it’s 14.7:1. We won’t get bogged down in the details, it’s enough to know cold air is rich in oxygen (air) and that’s what causes the hard starting. In order to fix this, the ratio must be adjusted.

A carburetor bike would usually employ a manual or auto choke to choke off the air but fuel-injected bikes do it a little differently. Instead of reducing air intake, they add extra fuel which has the same effect.

Air temperature sensor

But in order to do this, the ECU must know what the temperature is and so as you may have guessed a faulty air temperature sensor (ATS) is high on the list of root causes of a hard cold starting fuel-injected bike.

Faulty Battery

A failing battery will often work just fine in the warmer temperatures of summer, but a faulty battery will always show its hand in lower ambient temperatures.

Lower battery voltage equals lower engine crank speed. So, although the engine is turning over (cranking). It may not be turning over fast enough to produce sufficient voltage to fire the spark plug or create enough combustion chamber compression.

You can usually tell by the sound of the engine not quite turning over as fast as usual, and if you feel that is the case, go ahead and jump start (Boost). Your ATV runs a regular 12-volt electrical system, the same as a car or truck. It is safe to jump-start from any 12-volt battery/vehicle (actually 12.65 volts but referred to as a 12 volt). A car, truck, tractor mower, etc commonly run 12 volt systems and are suitable for a jump start.


Connect in the sequence 1, 2. 3, and 4 and remove in the reverse order 4, 3, 2, and 1.

If your engine starts on a jump, you’ve found your problem. Go ahead and replace the battery. It’s in the early stages of failure.

Testing ATV Battery

Don’t have jumper cables? Not to worry, you can test your ATV battery with a simple voltmeter (DVOM) Digital Volt Ohm Meter. This test is easy and is a two-step process. First off, let’s check the battery is fully charged. We can’t test a battery that’s just low.

Your ATV battery, although known as a 12 volt, is actually 12.65 volts when fully charged. Your battery needs to be in excess of 12.5 volts to successfully run the second part of this test.

Step one – Set your voltmeter to 20v DC (Direct Current). Connect the black meter cable connector to the negative post (-) of the battery and the red meter cable to the positive pole (+) of the battery.

I’ve listed a dedicated battery tester and a DVOM meter here on the ATV tools page.

Check your readings:

Battery volt check

Any reading below 12.4 volts will require a charge before we can reliably test the battery as per step two.

If you need to charge the battery, use a smart charger if possible. I use a smart battery charger when I’m not using my kit. They cost less than $100 but will save you money in the long game. They’re called smart chargers because you connect them and forget them. The charger senses the battery state of charge and only charges when necessary, with no risk of frying the battery.

If you have access to only a regular battery charger, that’s fine too but we’ll need a mechanics hack. If your battery is too low, a regular charger may not turn on, it’s a fail-safe setting which we can overcome with the hack.

Battery charging

Charger hack – Use jumper cables to connect a fully charged battery to our flat battery, then connect the charger and turn it on. This tricks the charger and starts the charging process.

The jumpers may be removed after twenty minutes. Total charge time depends on the amp rating of the charger and how low the battery is 3 – 4 hours is typical.

Step two – Assuming your battery is above 12.4 volts, go ahead and connect your voltmeter as before. At this point, you’ll need a helper to crank over the engine. If your DVOM has a min-max capture feature, that would be useful. If not, check for the lowest reading on the meter as the engine cranks for about 3-4 seconds.

Battery crank test

If your reading is below 9.6 volts, your battery has failed the test and will need to be replaced.

Stale Gas

If your gas is stale, and by stale, I mean older than one month, then it’s lost its Oomph and will cause starting issues. Cold weather starting only exasperates the situation.

ATV gas tank drain

Only you know how old the gas is, but if you think this sounds like your problem. Go ahead and drain the gas tank and replace it with fresh gas.

You may also need to drain the carburetor gas bowl, which is easy on most ATVs. (covered below)

You can prevent stale gas by using a gas stabilizer. It’s a fuel additive you can get in any auto parts store. Mixed with the gas, it helps it keep its ZING for up to two years and protects your fuel system from gumming.

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

ATV gas stabilizer

I use it in all my kit, two-stroke, and four-stroke engines, chainsaws, leaf blowers, hedge trimmers, tillers, mowers, and my ATV.

Choke Needs Adjustment

Most manual ATV choke controls are operated by braided inner with shielded outer cable (like a bicycle brake cable) and will need to be adjusted over time. Even though you’re pulling the choke plunger all the way out, if your choke needs adjustment, then your choke plate isn’t closing fully.

Testing manual choke – The manual choke for many ATVs is a metal flap that mechanically closes to obstruct the carburetor’s airway intake.

Choke adjustment

However, some may use a manual plunger type, both types are commonly activated by way of cable and lever and require adjustment from time to time. Go ahead and check the scale for slack and adjust as necessary.

You can check this by removing the carburetor intake trunking and operating the choke to full, and checking the position of the choke plate. Adjusting is pretty simple. Some models will even be toolless. It’s a matter of taking the slack out of the inner cable by adjusting the outer cable ends further away from their mounts.

Testing auto choke – Your choke may be auto, in which case a thermal control solid-state unit such as a plunger is employed and is located in the carburetor. This will need to be removed and tested.

Choke plunger

To test the plunger, disconnect, remove and measure plunger length. Reconnect electrical harness and measure again, must be within manufacturers spec.

Testing air temp sensor – Air temp sensor is crucial to fuel-injected engines for smooth cold starts.

Air intake temp sensor resistance test

Remember this is just an example, your bike spec will be different and exact spec is important.

Your air intake temperature sensor is located in the intake trunking or in the air filter housing. Check all wiring is secure and if you have access to a voltmeter, we can check the resistance of the sensor and also the ref voltage and return voltage. But you will need your bike’s specs, specs from another bike won’t match and will serve no use.

Frozen Carburetor

If your temperatures are very low, we could be looking at a frozen gas tank, carburetor, and/or gas lines. This condition, for most, isn’t common. However, if you are one of those hardy souls who live and work in extreme sub-zero temperatures, you may have found your problem.

Dirt bike carburetor bowl drain

So how do you know if your gas system is the problem? Try draining the gas bowl on the carburetor. If the flow is barely a trickle, it’s likely your gas is frozen.

Why does the gas freeze? The gas doesn’t freeze, but the moisture in the gas does, and this blocks the flow of gas to the engine. All fuel has a certain amount of moisture in it, and the engine, under normal conditions, doesn’t have a problem burning it off. But when the temperatures get very low, excessive moisture can cause problems.

How do you fix a frozen gas system? You have a few options. If your gas tank is low, top it up with fresh gas, the warmer gas will help unfreeze the system. Move your ATV somewhere warmer, or use a hairdryer or heat gun to unfreeze the carburetor and gas lines.

Use ethanol gas. Usually, I’d say ethanol gas is a pain, but in these conditions, it’s actually helpful. Ethanol is hygroscopic, it absorbs moisture in the fuel system. It also helps to keep your gas tank full, less empty space inside a gas tank equals less moisture on the walls of the tank.

Gas stabilizer

Use a gas stabilizer to help keep gas fresh and repel moisture.

In extreme conditions use a product like HEET. It’s a concoction of fuel and antifreeze and will unfreeze your fuel system and remove the moisture. In low temperatures mixed with your gas, this stuff will prevent freezing in the future. It’s easy to use, comes in a small bottle. Mix it as per the directions, dump it in the tank, job done!

Wrong Oil Type

This might not seem like it’s a probable cause of your cold start issue. But in cold weather, incorrect oil weight or too much oil can cause a slow crank speed as the battery and starter motor struggle against the heavier oil.

Oil temp chart

And as you learned earlier, a slow crank speed can prevent the spark plug from firing with enough intensity to start your engine.

Can you put HEET in an ATV? Yes, HEET is perfect for all four-stroke engines. It won’t affect emissions or damage modern ATV fuel-injected gas systems.

You may find the following posts useful:

Will bike start without kill switch?

Start a flooded bike

How to jumpstart an ATV?