Hi, I have an 02 trx400ex and recently purchased an fmf exhaust system ( power bomb header and powercore 4 muffler). I am just wondering if I would have to change the jetting in the carb to suit the new exhaust system. Also will the new system add any noticeable power at all? or just a nice sound.

 

you will have to change the jetting and yes it will improve the power. I'm a big fan of that system as well as the new lonestar exhaust systems

 

ok, but how will I know what kind of jets to put in it? or will there be a manual or something with the new system. Will the machine still run though even if I dont change the jets right away?

 

Yes your machine will still run just a little lean I have white brothers on my 400 ex and stock jets for now with a k and n filter and it rips wheels up first three gears and yes if it's a new system the manual should have jetting instruction