Hey STG! This is the first time I have heard mention of stretching the spring in the pump. I suppose this is to increase pump pressure. Could this be part of the reason I need to use the restriction in the bypass line? That engine is going back on my flying wing, and the tank is close to the engine. It will be interesting to see if it acts any different with shorter fuel lines.

raimondi STG and I have the same setup, with the exception of the muffler. He's getting a few more revs than I am with a bisson pitts, but the engine runs sweet with this setup. It will take a little tweaking to get it right, but it's not much work, and it is definitely worth the effort. I had to restrict the bypass line to the tank to get enough pressure to the main needle. Once I did that, all is well.