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ATV Carburetor Flooding (Top 7 causes)

You can’t mistake the smell of raw gas, and in the case of a gas leak, that’s a good thing. Leaking gas and hot exhausts aren’t a good mix.

There may be a number of reasons ATV carburetor floods with gas. Here are the top 7 causes:

  1. Worn carburetor float needle & seat
  2. Float out of adjustment
  3. Split fuel lines
  4. Loose line clamps
  5. Worn carburetor bowl gasket
  6. Stuck choke
  7. 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 an exact, mission-critical bit of kit. Any faults will make themselves known 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 let gas flow in. As the float rises, the needle valve closes again.

ATV carburetor needle valve

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 is 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.

2 Float

The float, as you know, acts on the needle and, in combination, directly controls 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.

ATV float adjusting

As carburetors age, the float tang gets weak and 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 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 are a common cause of fuel leaks, but over-tightening clamps can cause leaks too.

Gas line clamp

Loose, corroded, or missing fuel line clamps are 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. Paper and rubber gaskets can wear out, especially if the bowl has been on and off a few times.

Bowl gasket

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.

Choke adjustment

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 components removed. Most engines will run with the timing out just slightly, which can cause some very odd symptoms, including leaking gas.

ATV Timing Check

Remove your flywheel viewing cap and cam cover and check carefully cam sprocket marks (OHC engines) when at TDC.

Twin cam ATV engine timing marks

Here’s a typical twin cam setup. If your timing makes don’t align, you’ll need to reset the timing.

You’ll find the tools I recommend here on the ATV tools page and you’ll find common spare parts here on the ATV parts page.

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