Stand on the side of the bike opposite the petcock. You will see a black cover on the back of the carb, you will need to remove this first. Then look closely and you will see an allen head bolt (3mm?) going in at about 8 o'clock at a 60 degree angle. If you open the throttle while looking where the cover was you will be able to see the stop and the stop plate on the rotating assembly.
I cut mine down to the threads, but have seen others talking about 60%. I am not sure how that relates to what I did.
Take the whole top off and pull the baffle out of the exhaust.
99 WR400f, White Bros E-Series silencer and tapered head pipe. YZ seat and tank. Thumper rad guards, works frame guards, scots steering damper. Soon to be MX-Tech suspension. SETRA, AMA, Happy Ramblers MC.
97KDX220, FMF Rev pipe and silencer, renthals.
Courage is not the absense of fear. It is the judgement that something is more important, than fear.