ATV Carb Leaking Gas (Fixed!)


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.

  1. Faulty carburetor needle
  2. Float stuck
  3. Float Faulty
  4. Dirty gas
  5. 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 how to fix them, right now.

1 Faulty carburetor Needle

The carburettor bowl fitted to the base of your ATV carburettor, 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 fill the bowl.

As the bowl fills with gas, the float raises and causes the needle to seat, blocking the fuel orifice once again.

What’s the problem with needles?

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 carburettors consist of a needle with a seal incorporated, others may employ a needle with seal in the seat.

The rubber seal is what causes the issue, they become perished and develop cracks and split. A damaged seal will as you can imagine continue to allow gas fill the bowl.

When the bowl over fills, it will exit the overflow pipe if fitted, if not it may continue to fill the carburettor and flood the air box or cause a condition called Hydro-locking where gas fills the cylinder.

Common Symptoms of leaking needle include:

How to diagnose a leaking needle: Turn gas off and remove the bowl. Some carburettors may require removal to remove the bowl. With the bowl removed turn gas on and lift the float, if the needle continues to leak you found the root cause of the problem.

How to fix:

Fixing this is pretty simple, and you can easily take care of this yourself. Order a complete carburettor repair kit, if your model has a carburettor seat with seal and o-ring seal, be sure to change them out too.

To fit needle, remove the float pivot pin and the needle comes too. If your model has a replace able seat replace it too, together with 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 carburettor bowl and it determines the level of gas in the carburettor bowl.

Parking your ATV on very steep hills or loading it onto a flatbed can upset the float inside the carburettor 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 stabiliser in the gas and fill the gas tank it prevents lots of winterising 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 the upper level to a point where the gas floods the carburettor.

If your float is a one piece plastic unit, its not adjustable and must be replaced if causing issue.

How to diagnose maladjusted float:

The procedure is similar to checking for a faulty needle, (lift and check for leaks) but also check for free play in the float tang to needle.

With the bowl removed, you can also measure the float drop and check 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, they’re 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 manufacturers 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, valve and seat before refitting. 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 a 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 lager 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 carburettor.

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

Carburettors use gaskets to help seal individual carburettor components. A rubber or paper gasket is commonly used to mate and seal components.

The two most likely carburettor 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 carburettor 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 the to leak.

How to find the the leak:

Turn off the gas at the petcock, dry the carburettor of excess gas. Use some baby talk on the gasket areas turn gas back on and look for the damp patch.

A carburettor rebuild kit will include all the gaskets. Lube them lightly before fitting and don’t over-tighten.

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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