Bill,
I have never had a problem with muffler pressure when running pitts mufflers with two and four strokes. I run Clines with four strokes all the time, mostly with straight pipes. I drill/tap and install a pressure fitting about a 1/4" from the jam nut on the header pipe, and that works awesome. If you talk to Jim Cline, he will tell you to get your pressure from there. Also, A cline will work awesome with a two-stroke and pitts muffler, you are suppose to use crankcase pressure to start with anyway on a two stroke.
