my77stang

a double pumper will have one of these on both the front and rear bowl



and a vacuum secondaries carb will have one of these things on the side (the large flat shiney square thing with the circle on the left)


if your carb has "V" shaped bowls like in the first pic with a fuel line that connects in two places its a model 4150, if its like the second picture with squared off bowls its a model 4160.

splash21

ok i stand corrected. it WAS a double pumper but it was made into a vaccum secondary. i can see where the other pump used to be and i assumed it was still there for some reason. it is the v-shaped though

my77stang

all bowls are cast for the pumps, but holley doesnt machine them unless they are going to use it as a DP - so it was always a vacuum secondary carb[8D]

if you give the model number off the choke tower i can look it up and tell you exactly what it is.

67mustang302

It may have a diaphragm pump on the bowl for a DP setup, but the carb main body determines whether it's vac or mech 2nd. It can't be changed.

As for the OP's setup, a 650-750 carb would work well, but there's really no need to go bigger than a 750, even turning 7,000rpm.

FLcracker9

600 - 650 should be plenty. Brand is personal preference, I like Demons because they're easy to tune (I run them on 2 different vehicles), although Holley has copied some of their features on their new carbs.