[Charlie ny]

40,
Ken and I both use Daytona Parts accelerator pumps....correct
length and leather piston. We also exclusively use brass seats and
stainless needles unless requested by customers not to. I make my own
kits up for my own use and have settled on genuine Holley power valves
which require a bit of machining inside the bowl for head clearance. I've
used other PV's until recently but....well. My PV choice is 3.5 "/hg.
I've mentioned this in the past but think it may be time to say it
again. The heart of the 94 style carb is the vacuum operated PV. This
device really sort of reads what the motor wants by the presence or lack
of vacuum. Repeatedly the fly in this ointment is the bottom of the bowl
which forms the critical vac chamber with the iron base. It is not unusual
to find this face from .010 to .030 out of flat making a long lasting vac
seal tough. The top face of the base and the bottom face of the bowl
should be absolutely flat so that a minimum thickness gasket will be
properly squeezed and form a good vac tight seal. My choice is to
MACHINE these faces flat....I'm too clumsy to get this right with a
file.
Vacuum holds the PV closed, lack of or reduced vacuum allows
the valve to open. Lack of vac occurs when you jump on the gas
such as in passing situations or drag racing...your motor needs extra fuel
and the PV opens and supplies it. IF the carb has a vac leak between
base and bowl the PV will inadvertently open because it doesn't know
that the lower vac is due to the leak and not the motor under a load.
Like most Flathead components the carbs are pretty simple it's
just the little obscure details that muck things up.
Charlie ny