turned out to be the repro fishtail silencer restricting performance.......got an extended drill bit and drilled a series of holes in the end plate of the internal baffle support tube which improved things considerably.
This suggestion is well worth looking into. I had to do the same thing to a pattern BSA
BB34GS silencer some years back. It came with a very restrictive 5/8" (.625") hole through the baffle plate. I cut this out with a 1" hole saw from both ends completely removing the section of perforated tubing with the tiny through passage. Surprisingly, the end result wasn't that loud and the bike runs great.