I just bought a new YFZ 450 and I've got FMF pipe coming for it. Will I need to rejet it when the pipe is installed? Thanks

 

to make it run at its best you probably should but i dont think you have to do it

 

if you leave spark arrest in it then no, but the yfz is easy to jet, you know u want the extra power

 

Yes you have to. If you don't your yfz will have more flow than factory. It's already slightly lean at factory jetting. More air + less fuel = running hot.

Besides that if you don't you just spent that money just to change the sound. You won't get the amazing power increase without changing the jetting. It's not hard at all. Go ahead a pick up a air filter kit to replace the crap yamaha one and rejet. Your jaw will drop when you find the difference these 3 simple things can do.

 

sometimes if you buy an aftermarket pipe you can get away with running it without rejetting but if you change your airfilter to an aftermarket one or you run it without the lid then its very important to fatten it up, running your bike to lean is not a good thing, its better to be rich than lean.