You can’t mistake the smell of raw gas and in the case of a gas leak that’s good thing. Leaking gas and hot exhausts aren’t a good mix.
There may be a number of reasons an ATV carburetor floods with gas, here’s the top 7 causes:
- Worn carburetor float needle & seat
- Float out of adjustment
- Split fuel lines
- Loose line clamps
- Worn carburetor bowl gasket
- Stuck choke
- Timing off
In this post you’ll learn about the most likely reason your carb leaks gas and what you can do about it. You’ll also learn about other possible causes and what you can do to fix them.
1 Needle & Seat
Your carburetor is a very precise, mission critical bit of kit, any faults will make them selves know pretty quickly.
Leaks are common, the float needle and seat are the usual cause. Your carburetor has a fuel bowl which is a reservoir that stands ready to feed the motor with gas.
As fuel leaves the bowl, it must be replaced. The carburetor float, needle and seat maintain the bowl fuel level.
The float (usually plastic) pivots inside the fuel bowl and rides on top of the gas. The float needle is controlled directly by the float.
As the gas level drops, the float falls which allows the needle valve to unseat and allow gas flow in.
As the float rises, the needle valve closes again.
The needle and its seat must make a good seal. If they don’t, the fuel bowl will overfill and cause gas to leak from the carburetor or flood the cylinder.
The needle or the seal are fitted with a rubber seal, the seal simply perishes or cracks with age.
Replacement seal and seat aren’t difficult to fit and are available for most carburetors.
The float as you know acts on the needle and in combination, directly control the level of gas in your bowl.
Most floats are fitted with an adjustable tang, bending the tang adjusts the contact point and therefore the bowl gas level.
As carburetors age the float tang gets weak and simply drifts out of adjustment. Too much gas in the bowl will either leak from an overflow or fill your cylinder.
Replacement floats are available too and are easy to fit.
3 Gas Line
Don’t discount the simple fix, a perished gas line is soooo common and a it’s a quick fix. Check your gas lines from tank to carburetor for fine cracks and splits. Check your petcock (fuel tap) too.
4 Loose Line Clamps
Loose, corroded or missing fuel line clamps is a common cause of fuel leaks, but over-tightening clamps can cause leaks too.
5 Bowl Gasket/Seal
Your bowl is fitted to the base of your carburetor and uses a rubber or paper gasket to seal the union. Both paper and rubber gaskets can simply wear out especially if the bowl has been on and off a few times.
The exact source of leaking gas is often hard to spot. Try dusting the outside of your carburetor bowl using some flower or talk and look for the wet patch.
6 Choke Stuck
A choke that’s stuck in the on position will cause the engine to flood with gas. This is only applicable to some engines and only to those that have been repeatedly cranked without starting.
Check that the choke is moving to the off position, and adjust if necessary. Remove the spark plug and crank over the engine to dry the cylinder. Clean the plug and refit.
7 Timing off
This isn’t very common but worth knowing if you’ve had some work done and had the timing off. Most engines will run with the timing out just slightly, which can cause some very odd symptoms, including leaking gas.
Remove your flywheel viewing cap and cam cover and check carefully cam sprocket marks (OHC engines) when at TDC.