I have to chime in on the side of MVVS. I have 2 40's and the 49. That 49 is the hottest 45 - 50 motor that I have been around. Yes the needle settings are tempermental. Sean, are you setting your high speed needle with a tach? Peak the RPM - actually watch it drop 100 or so on the lean side and then go 200RPM rich from the peak. If you are not taching it, tweak the needle 1 click at a time until you hear the motor start to sag slightly and then back off a few clicks. You can easily be too rich and be fooled by the transition on to the pipe when you are setting the needle. With the mini tuned pipe, the transition on to the pipe is pretty abrupt. There is a chance that you may be running too rich and loading the engine with fuel in flight and then it falls off the pipe.

Dale