The jp pipes do not produce the best power on the go engines but it shouldn't effect tune of the engine, you may just need to take it out in the street and just work on getting it tuned. The novarossi carb should also not be making it harder to tune unless the carb itself or you tank/fuel line have an air leak.

But to answer your question the best pipe for that engine is the Go 801, then Go 2047, then Dynamite 086