RE: tuning the carb and pipe
Tune the carb, then shorten the pipe in small (1/4") increments until you notice that when you corner at wide open throttle the speed drops off, then back it out 1/8" at a time until you get the speed & power back. Once you have the length right, cut off the excess header inside the pipe so that 1/2" is left poking into the pipe behind the rear cooling O-ring. This way you can have some room for adjustments as changing props may need slight pipe adjustments, and if the pipe works back while running you won't lose your cooling of the O-rings.