If you change the pipe or do airbox mods, you definitely have to rejet. The motor will be breathing much better, which means that more air is traveling through it than before at the same RPM, which means it needs more fuel (this is why it will have more power, it burns more fuel per revolution). I had a local two stroke motorcycle racing mechanic do mine just so I could quit worrying about it being right.

 

we use to have a 97 TB 250 with HPD pipe and
clutch kit.HPD's kit works great it would beat my sport off the line when it was stock but the sport would walk it in a few seconds.
there is a pic of our TB 250 at my web site

 

How hard is it to replace the jets. I'm assuming you have to adjust the carb when doing that?