When the temperatures drop, ATVs can struggle to start. There’s a good reason for that, and the fix is usually simple.
Starting an ATV in cold weather will require fuel enrichment. Some ATVs do this automatically. Others use a manual choke lever or fuel primer. To start an ATV with manual choke type:
- Apply choke lever
- Don’t apply throttle
- Crank over engine
In this post, you’ll learn how to start your ATV in cold weather, why it struggles when the temperatures drop, and you’ll also learn the common problems and fixes with ATV engines as the temperatures drop.
What is AFR and Why is it Important?
When trying to figure out what’s wrong with an ATV that’s struggles to start in cold weather, it helps a little to have a basic mind map of what’s going on. I’ll keep this light, I promise.
Your ATV engine likes an AFR of 14.7:1. It means for every 14.7 parts of air (oxygen) your engine gets, it also needs one part gas. If this ratio is off, your engine runs poorly.
ATV engines traditionally employ a carburetor and its function is to mix air and gas to the correct ratio for any given throttle demand. Carburetors have served us well, but they are mechanical and suffer from wear and tear. More modern bikes use a car-derived computer-controlled fuel-injected system.
You’ll learn a little more about fuel-injected systems below but in this post, we focus on the more common and troublesome carburetor system.
Why Do Engines Find Cold Weather Starting Harder?
You already know engines love a particular AFR ratio and you know they protest if they don’t get it. Colder temperatures cause problem starting because cold air is oxygen-heavy, and that means your engine is receiving more air proportionally than gas.
Cold weather creates what’s known as a lean condition, meaning your engine is getting way more oxygen than gas, and if some form of fuel enrichment (choke usually) isn’t used it causes hard starting, stalling, or no start at all. You’ll often find a bike will be easier to start at mid-day, simply because the air is warmer and less oxygen-heavy.
Next, we’ll take a fast look at fuel-injected bikes before going on to look at the more common carburetor bikes.
Fuel Injected Fuel system
Some modern ATVs use a computer-controlled fuel injection system and while the AFR is still the target destination, how they get there differs greatly from a carburetor engine. Fuel-injected bikes use sensors, a pump, a fuel injector, a throttle body, and an ECU (Engine Control Unit) to make a ton of calculations about fuel supply. An air temperature sensor fitted inside the air intake box is crucial to cold starting.
The ECU is programmed to read air temperature before starting and adds more gas if needed, making the starting process automated.
Carburetors Fuel Systems
Carburetor bikes aren’t as clever as fuel-injected bikes, although some carburetor bikes use an auto choke, many are manual, meaning the rider needs to make a manual adjustment using the choke lever.
While a carburetor is seen as the less complex fuel system in some ways that’s just not true. A carburetor is like a wind instrument, it’s precisely tuned and like all mechanical kit, it wears and needs maintenance.
If your carburetor is out of tune you’ll experience poor performance or hard starting, bogging, stalling, flat spots, and the list of symptoms goes on and on.
Carburetor needs to be adjusted if
The AFR needs to be adjusted for:
- Cold-weather riding
- Riding at higher altitudes
- Humidity
- Bike engine modifications
Let’s now take a look at the common choke types.
Choke Types
Choke types vary, the most common types are auto choke, primer, and choke plate.
Auto choke – Most Auto chokes use some Thermo sensor and mechanical assembly to control the choke. An electrical mechanical plunger-type is common.
Lever choke – this type is a simple lever that restricts air supply to the engine. This has the same effect as adding more gas – it adjusts the ratio closer to stoichiometric. The disadvantage with this style is it must be turned off again.
Primer – the primer is the simplest of all to use, and lots of small engines mower chainsaws use them. A priming bulb is pressed, and it injects extra gas directly into the carburetor. This helps counteract the lean condition caused by the oxygen-heavy cold air.
Starting a ATV from Cold
It’s best to keep your ATV indoors, and that will help the starting process and make the start process a ton easier and it’s easier on your bike long-term.
First off, go ahead and determine if your bike is a manual or auto choke. A manual choke will be positioned on the handlebars or at the carburetor itself.
It will be accessible. You won’t need to remove any covers or panels to access it. You may need to dismount to locate it, however, but it will be accessible from the driver’s seat, usually on the left-hand side below the gas tank.
If you failed to find the choke lever, your bike might be an auto choke.
If your bike is auto choke, to start it:
- Turn ignition on
- Check Petcock set to “On” (fuel tap)
- Select neutral
- Slide kill switch to “Run”
- Pull clutch (some bikes)
- Hit start button
Don’t apply any throttle until the bike warms up. Wait 1 – 5 minutes, depending on conditions.
To start a manual choke bike:
- Turn ignition on
- Check Petcock set to “On” (fuel tap)
- Select neutral
- Pull choke to full or pump primer bulb 4-5 times
- Slide kill switch to “Run”
- Pull clutch (some bikes)
- Hit start button
Don’t apply throttle until the bike warms up.
After the start, move the choke back to 1/2 and, after a minute or so, turn the choke off. The time your bike takes to warn up varies by engine size and how cold ambient temperatures are. Hiccupping and popping through the carburetor means your engine is running lean, it’s not up to temperature yet and still needs a little choke.
Extreme Cold
I lived and worked in Canada for a few years and have had some small experiences of extreme cold temperatures. If we’re talking Brrr temps here, you’ll need to borrow a hairdryer or a heat gun. Start by warming the carburetor area for a few minutes (without damaging any plastic/rubber components), then direct the hot hairdryer air into the intake duct, may need to remove the seat.
Now attempt to start the bike as above, keep the dryer on the air intake until she warms. Living in these kinds of temperatures takes a special kind of tough, both human and machine.
A block heater for your bike is an easy mod that will pay off big-time.
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- About the Author
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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.