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.

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 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 fuel to the air 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., lacks gas).

The solution to the problem is to 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 air supply to the engine and is manually adjustable.

The choke is basically a metal flap that manually closes to obstruct the carburetor’s airway intake.

You’ll often find the engine will depend on ambient temperature only require a little choke to start, and on other mornings it may require full choke to start and then 1/2 choke for a few minutes until the engine warms up.

Modern ATVs may have an auto choke set up, and some very sophisticated models control modules with electronic fuel injection. They readjust the AFR automatically in cold temperatures, not by restricting airflow but instead by sending extra gas to the engine.

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.

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.

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, we should roll. It’s never a good idea to drive with the choke on as the engine isn’t yet up to operating temperature.

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. So you can safely jump start from another ATV, riding tractor, car, or truck. All run the same 12 volt electrical systems.

If your Quad 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 are above 12.5 volts when running 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. Check your readings:

  • 12.7 volts 100% charged
  • 12.4 volts 75% charged
  • 12.2 volts 50% charged
  • 12.0 volts 25% charged
  • 11.9 volts discharged (Flat)

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

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.

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.

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.

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.

You can prevent this from happening in the future 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.

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.

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.

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.

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 I don’t use ethanol gas, but in these conditions, it’s helpful. Ethanol is hygroscopic. It absorbs moisture in the fuel system. It also helps keep your gas tank full. Less empty space inside a gas tank equals less moisture.

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 can cause a slow crank speed as the battery and starter motor struggle against the heavier oil.

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

Related Questions

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.

John Cunningham

John Cunningham is a certified mechanic and writer on ATVFixed.com. I’ve been a mechanic for over twenty-five years, I use my knowledge and experience to write articles that help fellow gear-heads with all aspects of ATV ownership, from maintenance & repair to troubleshooting.

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