Hmmmmmmmm. Well here is my best guess for the moment, I would check the
vacuum at Idle and then check the power valves on the carb you are using.
The power valve should be 1 to 1.5 in Vacuum rated below your idle
vacuum. Say with the big cam you have 8in Vacuum at Idle, power valve
should be 6.5 or so. If the car has ever backfired with this carb it could
have blown the power valve. This valve compensates for the loss of vacuum
when the butterflies are opened and provides fuel. Another is a Holley
trick. With a big cam sometimes you need to drill 1 small hole each on the
butterflies to keep the carb out of the transfer slot at Idle which can
cause surging. I have a mostly stock 600cfm vacuum secondary carb which
runs perfect on the motor, just dosent have the top end kick of a double
pumper. I have an excellerator series 600cfm double pumper on the motor
that I have been trying to dial in. I have the same off idle cruise surge
that you do. Distributor is a factory dual point with electronic ignition
installed. Found a problem a while back where the advance weights were
sticking which caused a drop off of power after 3000rpm. I would also
check the rear butterflies, they have an adjustment screw which is used to
set their position at Idle, this might be to far and drawing too much
fuel. I will continue to ponder your problem in the hope that I can come
up with something to help you and possibly help me. :)
Good luck
Bill
b9470735
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