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1994 400l two stroke. I just had the piston and rings replaced because i lost compression. After the parts were replaced it started to backfire and wont stay running. Any idea what the problem could be. Thanks for your help.
 

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sounds like you are either getting too much fuel or too little fuel.

how long has it been since anything has been done with the carbs?
 

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and im guessing whoever jetted it did so according to relevant temperature and elevation for where the quad is?

was the carb pressure checked before it was installed again?
 

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Check the carb boot where it mounts to the cylinder. After pulling the carb, I had one that the rubber cracked and was pulling air around it. They get brittle with heat and age.
 

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If it is bad enough then yes. I would tear down the carb and inspect for trash or gumming, 2 stroke carb are bad about that after they sit the oil from the gas being mixed will gum up the carb. If its not starting first put a new spark plug(bad about fouling), if still nothing take off your air box and spray a shot of starting fluid into the back of the carb, if it tries starting you then know you need to go through the carb. Do not use a lot of starting fluid to try and keep it running, it has no oil and could cause engine damage.
 

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Did the old piston break or crack? Seen it a lot, if the old piston has a piece of it break it will drop into the lower case and the crank will roll it around and crack or bust the lower engine case. Check right behind the carb on the engine cases where they join together, this is where they normally bust if they do.
 
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