[thirdgen455]

I bought a carb from a friend of mine, carb worked great on his SBC, he decided to swap to a 750HP. his car ran 7.40's in the 1/8th mile. so I bought it knowing it was a good running carb. it's a older 750 DP with the proform center. has 50cc pumps. 78 jets front and back and had 3.5 power valves. I ran my fresh rebuilt 469 with it as he had it. and it didn't idle. I thought maybe I needed to up the power valve to a 6.5 since that is what I ran on the last motor with the same cam. anyway it idled somewhat better but it still whats to idle over 100 and the vacume is going all over the place from 15-8 up and down. well I thought maybe I had a big fat vac leak. i put my hands over the carb poof car dies. ok playing with the air screws i get it some what working where it is idleing at 1100, not bad but the old motor would idle at 600-700.
OK I have never messed with one of these proform center's before and I decied to see what happends when i block the air off to the screw in air bleeds up top. the thing idles up and the vac gauge goes to 15 and steady.
What does this mean. do I need to jet it up?
do I need to put in smaller air bleeds?
need some help, a good base line to start with, so I can start tuning this thing.
Thanks guys!

[thirdgen455]

I bought a carb from a friend of mine, carb worked great on his SBC, he decided to swap to a 750HP. his car ran 7.40's in the 1/8th mile. so I bought it knowing it was a good running carb. it's a older 750 DP with the proform center. has 50cc pumps. 78 jets front and back and had 3.5 power valves. I ran my fresh rebuilt 469 with it as he had it. and it didn't idle. I thought maybe I needed to up the power valve to a 6.5 since that is what I ran on the last motor with the same cam. anyway it idled somewhat better but it still whats to idle over 100 and the vacume is going all over the place from 15-8 up and down. well I thought maybe I had a big fat vac leak. i put my hands over the carb poof car dies. ok playing with the air screws i get it some what working where it is idleing at 1100, not bad but the old motor would idle at 600-700.
OK I have never messed with one of these proform center's before and I decied to see what happends when i block the air off to the screw in air bleeds up top. the thing idles up and the vac gauge goes to 15 and steady.
What does this mean. do I need to jet it up?
do I need to put in smaller air bleeds?
need some help, a good base line to start with, so I can start tuning this thing.
Thanks guys!

[dutch injun]

I could only get my car running by closing up the butterflies even more, maybe you vacuum signal is weak...too much air goin in.

[tikiklubracing]

Always adjust idle screws before adjusting throttle stop screw, as screwing in the throttle screw will cause some bypass in the idle circut killing necessary vacuum to run the idle circut. Sounds like you need to turn throttle stop screw until butterflies are just closed then adj. idle screws. HIH

When usure ask. BIGGERISBETTER-78 Catalina 400 .060, 3.73 spool, :TH350. 15 yrs in NHRA tech ret. Check em out, www.nhra.com. or www.ihra.com or to find tracks www.chasinracin.com