I put my Euro style muffler back on and now my bike runs smoothly at any RPM I choose to run at. Therefore, using a stock, uncorked US pipe, which created a much more free-flowing exhaust situation, created a mis-jetted situation on my bike. So mis-jetted that the needle position by itself wasn't enough to fix the rough running. It still backfires though, so I will try the adjustments that have been recommended, (unscrew the pilot adjuster or get a richer pilot jet) but not till this coming weekend (ugh). Also, the more restrictive pipe does not allow me to bring the front wheel up as easily. Taffy, So, if I want more performace using the Euro muffler, I could try the jetting you have been discussing. I would probably need to modify your settings somewhat for altitude. Any thoughts? Anyway, I'm glad to be able to report a cause and effect so I can provide a little back to this great group.