I just purchased a used quad. When it is at operating temperature is runs great but when first started it pops and backfires untill it is completely warm is this normal? It has a FMF pipe and has supposedly been jetted for the pipe.

 

what kinda quad is it???

 

2002 400ex it was only about 15 degrees out when I bought it. The popping only happens when I give it gas when its cold.

 

I have a 2000 400ex w/ a FMF pipe also. I have experienced the same type of problems in the cold weather. I was wondering the same question.... I'm guessing that it is normal and it isn't normal all at the same time, if that makes any sense? I am looking into getting a dial a jet kit when it gets a bit closer to spring and I think that may help alleviate any problems that I have been having w/ mine.

 

The popping and backfireing is symptoms of lean .
It may be just as simple as leaving the choke at partially open til it warms up, or bigger pilot jet, or opening up the mixture screw. Id start by opening the mixture screw, another 1/4 turn and see how much it helps.
Does the air box still have a sealing lid on it...or is it missing or have holes in it?

 

I second the fuel/air mixture screw idea. Ive had to mess with mine for the same reason a couple times (when temps go from one extreme to the next)