On the exhaust discussion, there are a couple ultralights with 2-strokes at the airfield where our EAA chapter meets that don't even resemble anything like a tuned pipe. Now granted, they are more than likely not reaching "spec" HP, but they do run and manage to pull the ultralights through the air. Maybe I'm wrong on this, but if a 2-stroke's pipe design is "off" it'll make the engine run at below it's potential HP, or, it will blow un-burned fuel out the pipe. If EGT and CHTs in the process aren't causing damage to the engine in the process, it just results in a engine that's down on performance from what it could be. It might result in excessive engine wear, fouled plugs, and other ailments, but they do run. In reality, any 2-stroke that's being run at an RPM outside the range of a pipe's "tuning" is running below it's performance potential, either wasting fuel or not evacuating all of the exhaust thereby not developing all the HP it could.
There's my opinion on it, and consider it's probably worth the price paid. $0.00 :gig:
Lynn