I have the red Perry pump on a Webra Speed .40 with a tuned pipe. I can tell you that the pump works great! The Webra has a Dynamix carb, which doesn't have the greatest fuel draw (But big bore diameter for lots of power). I set my engine a tad rich on the ground, and it maintains a consistent needle setting during the entire flight. I have never had a sag because of the engine going lean. I don't have any muffler pressure coming off the pipe, so I know it must be the pump doing it's thing.