Is the exhaust 1" copper tube???
Im sure that if you played around with the exhaust a bit you could get a bit more power out of it.
Where it comes out of the cylinder get a fitting that keeps the OD the same all the way through the first bend down. Step it up to a bit biger than an inch for about 8 inches or so then back down to 3/4" to the exit port on the leg.
Use the shape of a motorbike expansion chamber as a guide.
Would take a bit of trial and error to get it right but through that and jetting you could easy get 50% extra power.
