There is good reason not to mess with it. It comes from the factory with the best overall setting. Any adjustment to it will only make it worse. There are of course exceptions. Manufacturing tolerances, an unusual fuel/pipe/engine combination or really radical timing changes (mods) to the motor could cause a need for some fine tuning on the spray bar. I can almost always get a motor running properly without touching it. I can only think of two times in the last ten years that I had to make some spray bar adjustments to get a motor to run right.