Ask the Editors: Exhaust Pipe Full of Fuel

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Why is there gas going into my pipe?

Dear ATVC: After just rebuilding the top end of my 87 Suzuki LT250R, I put it all back together and now when I kick it a few times the exhaust fills up with fuel. I’ve checked over the whole carb and it’s working fine. I’m unsure of why so much unburnt gas would be running into my exhaust. I was told to check the reed but other than that any suggestion would be great. Mitchell9997

You are indeed honing in one of the two most likely possible culprits. We’re more inclined to think it’s a carburetor issue despite the fact that you said you gone over it. You may want to take another look to ensure that the float is clean and operating smoothly.

A faulty or sticky float valve won’t necessarily cause an obvious leak (like coming in to find fuel all over the floor) but it can cause gas can run down the intake port and fill the cylinder. Since 2-strokes lack valves that have to open to release this fuel, you kicking the piston up and down can push all of that gasoline directly out of the exhaust port and into the pipe.

If indeed the float checks out, then the reed valve is your other major possible cause. Obviously a cracked or chipped petal will solve this riddle immediately, however, oftentimes reed valves can malfunction without such observable damage.

A bent reed or even one simply worn out of tolerance can also lead to fuel bypass. Replacing the reed would likely immediately solve your problem if this were the case.

Lastly, it’s very unlikely but a cracked head could also cause similar symptoms in rare instances but a simple compression test should be able to rule out this possibility. We’d certainly inspect the other two possibilities first.

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