My two cents worth. And FWIW I am really happy my FCR Another thought about the BST is it richens the mixture as the needle is raised by the diaphragm. The diaphragm is responding to pressure differentials of atmospheric pressure and engine vacuum. Alot of talk to say it raises relatively slowly. It does a good job of metering the fuel for what the engine can handle at varying loads. If you twist the throttle wide open at lower rpms the BST if tuned properly, only delivers the fuel the engine can handle. Now the FCR. No diaphragm but the slide and needle move in perfect conjunction with your wrist. What this means is you need to be in tune with your engine at lower rpms as it does not need the slide and main jet wide open. Sometimes a gradual increase in the wrist/fun factor is more beneficial than wide open. If the back tire can spin crack it hard. If you have good traction modulate the throttle and you DR will be happier.