RE: Rossi .45 problems
Smackie,
Solve the nitro issue first...
But the tuned-pipe is hardly a 'set and forget' endeavor as well.
Once you had set the length to suit a certain prop and fuel combo; changing something, or even a change in the weather, could make it necessary to readjust the length again.
I am not sure if the Rossi pipe is a cone-and-disk design, or a dual-cone design; but the later is less critical and the former very critical in this respect.
Earlier Rossi carburettors had a throttling issue, with the mid-range being way too rich...
The OS carburettor that you now have is too small for this engine and the top-end could be compromised.
It also has a richer than necessary part-throttle.