Auto Racing: my carb, double pumper, manifold vacuum

Question
QUESTION: i have a a 1963 c-10 with .30 over 350 with flat top pistons my cam is .480 lift and 280 duration 255 @.50 i have 292 angle plug heads that have been ported and polished with 2.02 valves a preformer rpm air gap manifould and a holley 650 double pumper carb i cant get it jetted right the best ive got it was 72s and 76s it ran ok but was very fat and would start to foul plugs after 5 or 6 runs but when i jet it down any it will sputter or hesitate when i stab it, i have a 3.5 power valve in it i know its a 13 second truck but ive only been able to get 14.47 (it dosent start to pull till 60ft my times are around 2.30 @60ft) out of it i only have a old protronics small cap distributor so idk if it flat out cant make enough spark to burn enough fuel to keep up with my heads and intake i race in spokane wa @ 3500-4500 feet of altitude will you give me some advice on jet or ignition ideas if you need more info just ask

ANSWER: First off I think you would do better with a vac secondary carb. For the cam you are running a double pumper is too much.
If you don't want to change the carb, You will need to do a few things to Band-Aid the situation. First, attach a vac gauge to the manifold and find out what the measurement is at idle. Your power valve is way to low for that cam. I think a 6.5 might help with the stumble. To eliminate a bog on full throttle launch you would adjust the shooters not the jets.
Please answer the following questions for me.
What model number carb do you have?
What is the manifold vacuum?
What is your timing set at?
What is the idle rpm?
Is the truck stick or automatic?
What gears in the rear?
Have you adjusted the curve on the distributor?








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QUESTION: my timing is @ 36 degrees, my idle rpm is around 1200, the manifold vacuum is at 7 inches, its a turbo 350 with 372 gears in a 12 bolt chevy rear end the carb number is 4777-2 and i have #28 shooters. i had a 6.5 in it and a 5.5 it didnt seem much better

Answer
Your idle is way too high for that cam. It should idle easily at 750. your manifold vacuum should be about 11-12 inches. Is your timing total 36 degs or do you have the mechanical advance locked so that it is 36 at idle? You should have the initial set at 12btdc at 750 rpms and a total of 36 all in by 2800 rpm. I think you have the primary throttle plates open too much at idle. You are no longer using the idle circuit and are now into the main jet circuit. On the underside of the Holley baseplate under the secondary throttle plate there is a flat head set screw. Turn this screw clockwise to open the secondary plates so that you just see the edge of the idle transfer slot. Now do the same for the primary using the main idle speed screw. Turn each mixture screw in until it seats.
Next install a timing tape on the balancer and rotate the engine until the 12 deg btdc mark on the tape lines up with the 0 on the timing tab. Remove the dist cap and align the rotor with the number one cylinder post on the cap. Tighten the dist clamp. Start the motor.
If it won't idle without you pedaling it advance the timing in 2 deg increments. Now make a full pass and check the plugs. Jet accordingly.