Peter,
Did you get the hi flow insert from me? If not you need to remove it and make sure the ends are "flush". If they are not, cut the perferated tube so that it is flush on both ends. If the tube is extended on the front side [towards the front of the bike],it will cause major turbulance and effect both power and gas mileage. I noticed several people have different concepts, but let me assure you I know about exhaust systems on the Whizzer motor. In fact the current insert is a close copy of an insert that Tom Hand [leading exhaust expert] and myself developed and tested approx 4 years ago. The insert was tested hundreds of times, and many of the times the tests were run on several different Dynos. Other than making the ends even, DO NOT make any other changes. If you drill extra holes, or remove the material the insert will perform much worse, I know this to be a fact. The untimate exhaust pipe on a Whizzer motor is 28 1/2" long [not counting the exhaust manifold in the measurement], the end of the pipe cut at a 45 degree angle [echo chamber cut off]. Just ask anyone that attended the dirt drags at Dawson Springs, Ky last month, how effective a tuned exhaust sytem can be.
Whizzer OuterBanks,
Quenton