I'm running a 11x7 APC today (had a zinger 11x7.5 yesterday but not enuf fly wheel to keep a low idle) and just took off my long homemade rubber muffler extensions.

I noticed an undeniable db increase along with a noticable speed increase-

I'm still running on the rich side cause of 15% all synthetic fuel and I'm using a coarse carb filter over the venturi and she's up to 11,650 rpm.

My low end is still fluctuating from 2200 up till 3000. Why?, I don't know.

Hope this info helps all.

root