Yes back pressure does make a lot of to do how a engine runs.It effects how they Idle, how fast they warm up and the top rpm is also effected. The photos below show a power exhaust valve, a bolt that is adjustable (varies back-pressure) and a photo of a exhaust valve I made for my DLE 30. It was linked to the throttle & would open & close at the same time. It seemed to work well for me. I could not get a manufacturer to bite on it? I still may make another version that will fit on the outlet of the semi -tuned exhaust. Capt,n