Gas coming out of exhaust pipe?!?

I just re-assembled a 79 Vespa ciao, everything went smoothly. I went to start it, and at first, it sounded like it was going to start, but it didnt, and wont. At this point I noticed gas/oil dribbiling out of the exhaust.

What could be causing this???

I had the cylinder bored out to accomidate a slightly larger piston (still 49cc). Im thinking (but hoping against) maybe the bore is slightly too big and too much fuel is getting by?

Anybody have any ideas?

Re: Gas coming out of exhaust pipe?!?


Well did you make sure you have a spark and all? If there isnt a spark to light the gas\oil\air mix then its just gonna shoot out gas and oil instead of exghaust. My friends mo-ped will do the same till if fires up. Then it goes away.

Good luck,

Trac Man

Re: Gas coming out of exhaust pipe?!?

Yes, I have spark, though Im not sure if it is strong. I checked the plug after 3-4 minutes of pedaling and it had gas/oil mix on it (like it should) but the plug was still sparking. I also tried a smaller, then larger gap, but to no avail.

Re: Gas coming out of exhaust pipe?!?

J. Sailor /

It sounds like a spark plug problem.

Re: Gas coming out of exhaust pipe?!?

If you have to pedal that long, there is definitely a problem somewhere. My Grande fires off on the third kick cold and on the first afterwards.

Your float or float needle may not be doing their job. Remove the carburetor and check these items.


Re: Gas coming out of exhaust pipe?!?

all you need to do is disconnect the muffler and drain it then take out the plug and dry it and before putting anything back on crank it over and over for about 2 minutes and the excess gas will be shot out the plug hole. the gas in the muffler is causeing it not to run and the gas is going all over the plug because its flooded and drowing the spark.

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