i just got a white bros e-series used for my 400ex, currently with a UNI air filter and airbox mod(same effect as no airbox lid) and a stock exhaust with baffle/spark arrestor cut off. im running a 42 low jet and 190 high jet, kiehin stock carb.

this is my first experience with an aftermarket exhaust. i know the basics with an exhaust system, more backpressure means better top end, less backpressure means better low end.

any tuning tips?

is it OK to run with no spark arrestor? my friend did it on his honda 100r and it made it a good bit faster.

im assuming that without the spark arrestor the plates lose their functionality, so there would be a very small difference with tuning with/without the plates if any at all, is this correct?