the problem is your engine needs more back pressure to make it run right and the new pipe is the cause,an expansion chamber exhaust lets the gas run so freely that the back pressure doesnt exhist below about 5000 rpm ,the cure is to fit some 4-5 gram variator rollers to the variator it will rev alot more when you go to pull away and therefore the back pressure will be enough to make your 2 stroke engine work as it should.rollers are very cheap about £10 for a set of 6 ok hope you happy now you know what the prob is.
adam bike doctor, March 2009
