I bought a k&n filter and jet kit for my TRX250 fourtrax and the main jet that came with the jet kit is a 92 my stock jet is a 95 if the k&n breathes better than would I not need a bigger main jet not smaller. If I run with the 92 that came with the kit will it hurt valves or piston if it is to lean ?

 

too lean will cause pinging (detonation) and will hurt the piston and whole upper end if severe enough. Where did you buy the jet kit from? you might want to call them and tell them your sitution because it sounds like somethings a little wacky. If you have a higher flowing air filter, then you are getting more air in the engine, so you need more fuel to compensate to make the ratio right. which means a bigger jet, not smaller.