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


I look forward to a heavy snow fall, gives me a excuse to ride the Quad, but for some the cold weather brings disappointment.

When an ATV won’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 ATV’s 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 in order to start the engine in cold temperatures.

Applying the choke creates just the right fuel to 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 the 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 air way intake.

You’ll often find the engine will depending 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 ATV’s may have an auto choke set up and some very sophisticated models run control modules with electronic fuel injection. They readjust the AFR automatically in cold temperatures, not by restricting air flow, 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 model to model but usually on the handle bars 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 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 feel 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 half way.

Most engines will be happy with 1/2 choke immediately after start, but if your engine stumbles and stalls, just give it some more choke until you find the sweet spot.

As your engine starts to warms, 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 at all and will run poorly if choke is on, (running rich).

Warm up time will be dictated by ambient temperatures but after 2 or 3 minutes we should go 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 it’s 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, if the engine isn’t 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, 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 jump cables? Not to worry, you can test your ATV battery with a simple volt meter (DVOM) Digital Volt Ohm Meter.

This test is easy and and is a two step process. First off, lets 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 be above 12.5 volts when running the second part of this test.

Step one – Set your volt meter 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 a $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 battery sate of charge and only charges when necessary, no risk of frying the battery.

Step two – Assuming your battery is above 12.4 volts, go ahead and connect your volt meter 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 just 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 you problem. Go ahead and drain the gas tank and replace with fresh gas, you may also need to drain the carburetor gas bowl which is easy on most ATV’s.

You can prevent this happening in the future by using as gas stabilizer, it’s a fuel additive you can get in any auto parts store. Mixed with the gas, it helps it keep it’s 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 your 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 check the position of the choke plate. Adjusting is pretty simple, some models will even be tool-less. 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 your 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 actually 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 if 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 hair dryer or heat gun to unfreeze the carburetor and gas lines.

Use Ethanol gas, usually I’d say don’t use ethanol gas but in these conditions, it’s helpful. Ethanol is hygroscopic, it actually 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.

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 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 effect emissions or damage modern ATV fuel injected gas systems.

John Cunningham

John Cunningham is an certified mechanic and writer on ATVFixed.com. I’ve been a mechanic for over twenty 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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