<<I know there is a proper tool to measure the amount of fuel that gets squirted out. Anybody knows if I can get / make one?>>
The proper tool is a graduated glass vial. I never messed with the pump volume on my 72 250 but I do know that the amount per stroke is critical, based on my experience with Weber triple throats on two Porsches. Those carbs were also used on the Ferrari Boxer which I never laid a hand on. RLE
