need help with BBC
 

I have my fresh 402 in finally.Its a .030 over 402 10:1 hyper. pistons , voodoo cam(272),performer manifold, new Holley 3310 750 cfm carb,new dizzy,wires ,etc,etc. having problem getting it to idle?? Have checked for vacumn leaks ,seems ok, starts right away ,but have to keep the gas to it to get it to idle . throttle runs up without stumble ,but comes down then stumbles and wants to die. Have adjusted curb idle up and down and will run at about 1200 rpms. Timing is set at 12 degrees. any lower and it wants to backfire back through carb. Any ideas??

Re: need help with BBC
 

Double check for a vacuum leak especially if there are ports in the carb for pcv or brake booster fittings etc. (I'm not familiar with your particular carb. Another thing that comes to mind is the firing order. I've been a mechanic for a long time and I know the chevy and ford firing orders by heart but I still cross two wires now and then. Hope this helps.

Re: need help with BBC
 

Id say make sure your dizzy is on TDC no 1. line up the balancer to 0 deg. then pull the cap to make sure your not out 1 tooth. it can happen so easy.

Re: need help with BBC
 

I'm betting on a vac leak. The vac advance diaphragm in the distributor is an often overlooked source . If it's ruptured or torn it will leak like crazy and you'll easily miss it on a quick check. Just a thought, Dean

Re: need help with BBC
 

Start it up and keep it running while spaying carb cleaner around the carb, if it dies or the rpm's go up you have a leak. It sounds like a vac leak to me as well.

Re: need help with BBC
 

On a fresh rebuild and new carb and dizzy. Alot of possibilities, Mine came back from a rebuilder and had a really rough idle, after carb idle adjustments(mixture) and timing set to 12* with no vacuum I went in and adjusted the valves that took what was left of the roughness out. With the 10-1 and the 272 cam it will be lopy at idle but a smooth lope. I was running stock 8.5-1 and a crane 272/284 cam idle was 750rpm to keep it from shaking to bad in drive, Neutral/park idle speed was about 850rpm.

Re: need help with BBC
 

You have a lot of cam there with the "272" (what is it at .050 ?). Run as much time as you starter will crank and run your vac. advance from manifold vacumn.

Re: need help with BBC
 

Hey guys thanks for all the replies. This weekend I'm going to check everything once again and see what comes up.

Re: need help with BBC
 

Put a vacuum gage on it and see what you have. May need to swap out the power valve. Take you vacuum reading, cut it in half. That will tell you what PV to run. Do you have the vacuum advance hooked up? If so, disconnect it, plug it off and then check your timming/idle. It is better to set your air/fuel mixtures with a vacuum gage and not by ear. Plug check. You should have no problem getting 12-15 inches of vacuum. If the gage jumps around, you have a vacuum leak. Do you have a auto or standard tranny? If you have a auto, and you drop it into drive, what happens? Does it die in park and drive?

Re: need help with BBC
 

Hey steve, I have an automatic 700r4 , and i do have a vac gauge. When i do put it in drive it does die unless you give it some gas. I check the readings this weekend.

Re: need help with BBC
 

Try disconnecting the vacuum advance, plugging it off and then set timing and idle. I don't run the vacuum advance at all. I just run a mechanical in the dizzy. Try going to about 16*, no vacuum advance. Do you have a stall?

Re: need help with BBC
 

not at present ,ordering a 2800-3000,,,,,next project

Re: need help with BBC
 

That will help for when you drop her in to drive. Try disconnecting the vacuum advance and set her up and she how she runs. It could be trying to advance too much at idle.