daweise1 wrote on 08/06/08 at 08:28:16:
the vacuum will "pull" based on right hand demand.
The vacuum on the petcock is only used to open the plunger via a diaphram. No real pull of fuel......
The Carb float and it's associated needle valve control flow rates. In theory, the float should have the bowl mostly full and the needle will be "almost" seated which would almost shut off flow most of the time . It would only have to really flow at WOT or at startup after sitting for awhile.
Your test of the OEM petcock flow rate...., drain the bowl, drop it, then hold a cup under it and turn the petcock to PRI for a period of time ( a minute???). Check how much came out. Note: I'm not sure if you can do this with the bowl on. Why?... the drain might not drain fast enough and if so... then the float might shut off the flow a little.....