Leaking gas is dangerous and obviously needs your immediate attention. The risk of your ATV catching fire is real, and if you park in a garage, the situation could be life-threatening.
The top 5 reasons for ATV carburetor gas leak.
- Faulty carburetor needle valve
- Float stuck
- Float faulty
- Dirty gas
- Faulty carburetor gaskets
In this post, you’ll learn all about the top five reasons your ATV carburetor bowl leaks gas, how to diagnose them, and what you need to do to fix them right now.
1 Faulty Carburetor Needle
The carburetor bowl fitted to the base of your ATV carburetor is a reservoir of fuel that stands ready to feed gas to the engine as it demands. The bowl contains two important components that work closely together, the float and the needle valve.
The float, as its name suggests, floats on top of the gas inside the bowl. It pivots on an axis and is directly attached to the needle valve. The needle (needle valve), which is a metal valve with a rubber seal (or the seal may be part of the needle seat), moves off its seat as the float falls. This opens an orifice and allows gas to fill the bowl.
As the bowl fills with gas, the float rises and causes the needle to seat, blocking the fuel orifice once again.
What’s the problem with needle valve?
The float and needle are in constant operation so long as the engine is running. Needle failure is very common. These guys work hard and are submerged in gas all their working lives.
Some carburetors consist of a needle with a seal incorporated. Others may employ a needle with the seal in the seat.
The rubber seal is what causes the issue. They become perished, develop cracks, and split.
A damaged seal will, as you can imagine continue to allow gas to fill the bowl. When the bowl overfills, it will exit the overflow pipe if fitted. If not, it may continue to fill the carburetor and flood the air box or cause a condition called Hydro-locking.
Hydro-locking – a condition where gas fills the cylinder and prevents piston movement.
Hydro-locking is more closely associated with water ingestion but is a common symptom of leaking carburetors.
If you find your engine does suffer from hydro locking be sure to change the engine oil after fixing the root cause of the issue (usually carburetor needle valve). The crankcase becomes contaminated with gas and dilutes the engine oil reducing its ability to protect your motor.
Common symptoms of leaking needle include:
- Leaking gas from carb
- Gas in the air box
- Overfull oil level
- White smoke from engine
- No starts
- Hard starting
- Black smoke from engine
- Misfiring
- Stinks of gas
How to diagnose a leaking needle:
Turn gas off and remove the bowl. Some carburetors may require removal to remove the bowl. With the bowl removed, turn the gas on and lift the float. If the needle continues to leak, you found the root cause of the problem. Go ahead and replace the needle valve.
How to fix:
Fixing this is pretty simple, and you can easily take care of this yourself. Order a complete carburetor repair kit. If your model has a carburetor seat with a seal and o-ring seal, be sure to change them out too.
To fit the needle, remove the float pivot pin, and the needle comes too. If your model has a replaceable seat, replace it too, together with an o-ring seal.
2 Float Stuck
You already know the float controls the needle valve and so it’s crucial to the fuel supply system. The float lives inside your carburetor bowl and determines the level of gas in the carburetor bowl.
Parking your ATV on very steep hills or loading it onto a flatbed can upset the float inside the carburetor bowl and cause it to simply stick in the lower position.
Overwintering your ATV, especially with an empty fuel bowl, can cause the floats to stick. I prefer to use a fuel stabilizer in the gas and fill the gas tank; it prevents lots of winterizing stale gas-related issues.
Anyway, if you suspect this could be your problem, the fix is simple. Park the ATV on level ground. Try tapping lightly on the side of the bowl. Try also bouncing the bike up and down. This should release the float.
If that fails, go ahead and remove the bowl drain bolt. If you can access the float, give it a little encouragement. Emptying the bowl and turning the gas on to refill will very often solve the problem.
3 Float Out Of Adjustment
Modern floats are made from plastic, but when I started as an apprentice, they were soldered metal float and gave endless trouble. Most modern floats are fitted with a metal adjustable tang that actuates the needle valve.
The constant movement bends the tang (made from lightweight material) downward, which has the effect of allowing more gas in, raising the upper level to a point where the gas floods the carburetor.
If your float is a one-piece plastic unit, it’s not adjustable and must be replaced if causing an issue.
How to diagnose maladjusted float:
The procedure is similar to checking for a faulty needle (lift and check for leaks) but also checking for free play in the float tang to the needle.
With the bowl removed, you can also measure the float drop and check the spec with your carb manufacturer. Other tools and accessories like clear pipe or transparent bowl made diagnostic a lot easier. But if in doubt, replace the float, needle, and seat, there aren’t expensive or difficult to fit.
Adjusting a float:
Remove the bowl and check for tang needle free-play. Removing free-ply may solve your issue, but it’s best to have the manufacturer’s specs for float drop and adjust to spec.
Removing the float:
Remove the float pivot pin. Some may require a small punch and some gentle tapping to remove. Others will just slide freely out.
Once removed, the needle valve will come also. Adjust or replace float, replace the float valve, and seat before refitting. If fitting a new float, the float tang should be set from new, but check for free-play before installing the bowl.
Adjusting the tang is simply a matter of bending using needle-nose pliers, refitting, and checking float drop.
4 Dirty Gas
Dirt in the gas tank can cause problems when it arrives at the needle. A fuel filter will catch larger debris, but crap still passes through the filter. Old gas lines perish and start to break down, and not just on the outside.
The inner walls of the lines break down, and small particles of rubber get trapped in the valve, holding it open. This, as you can imagine, allows the bowl to overfill and spill from the carburetor.
How to diagnose:
Check your gas lines. If they’re ten years old or more, they need to be replaced. Replace your gas filter too. An old filter will break down too and cause problems.
5 Faulty Gaskets
Carburetors use gaskets to help seal individual carburetor components. A rubber or paper gasket is commonly used to mate and seal components.
The two most likely carburetor gaskets to leak are the bowl drain bung gasket and the fuel bowl gasket. The reason for this is pretty obvious. They are the two carburetor components most commonly removed for inspection or repair.
The gaskets become brittle with age and are easily damaged. Over-tightening or pinching the gaskets on installation will cause them to leak.
How to find the the leak:
Turn off the gas at the petcock, dry the carburetor of excess gas. Use some baby talk on the gasket areas, turn the gas back on and look for the damp patch.
A carburetor rebuild kit will include all the gaskets. Lube them lightly before fitting, and don’t over-tighten.
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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.