I found a new Ron Woods low pipe racing MZ glasspack muffler, and installed it, pic attached. Lots more power, no stumbling, idles well at ~1200 RPM, and lot more noise.

I have the Bing vergasser. Alle is ok except for backfire pop when downshift and coast off-throttle through the new muffler. I think the vergasser needs jet change, possibly too lean on the pilot? No pop with the A2 muuffler before, but much more power now. How do I fix the backfire/pop through the muffler? Anyone done this or similar?
Also, I've never checked the valve adjustment. Could this also be causing the backfire? I know it's hard to diagnose as the possible causes are numerous, but I very much appreciate the advice of the experts here. Danke, Donny
