My memory is getting pretty bad lately and its been some time since dealing with my original type muffler...I do recall replacing the inner pipe and remember drilling a lot of holes that were larger then original, I can't recall capping off that inner pipe or if it is even suppost to be capped off, I wanted as little back pressure as possiable....One other thing I did was to open up that exhaust exit slot in the bottom back of the backbone tube/muffler housing, to me It seamed that that was a sizable restriction.
My A-22 has always ran or sound like it has an exhaust restriction or ign timing that you can't quite get dialed in just right....However for some reason on a cool damp morning that all goes away and she runs pretty strong?