I got my Chevelle on the road today for the first time since putting the engine back in with new heads and a new 4200 stall converter. I took it out for about a 10 mile drive over to my parents house and it ran great. Comeing up to stop lights it idled just fine in gear. I was at my parents house for about 2 hours and when I went to leave, it started fine but when I put it into gear it dies within 2 or 3 seconds. I even raised the idle way up to about 1600 rpm and still no good. I can get it to stay running in gear if I play with it, but it is tough and no way driveable. I had to have it towed home! The ignition system is a Holley Annihilator digital ignition that has a computer that controls all the timing so there is no vacuum or centrifigal advance. The rest of my combo is listed in my signature. I am at a loss here... I dont have the slightest idea where to start looking.

Any help is greatly appreciated! Thanks in advance,

Dan

I had this once and found my intake was leaking vacume at the rear of the intake where the cork gasket usually goes. Fun part is, you have to pull the intake to even check for it.

sounds like a big vacuum leak started somewhere. Is there a 3/8" diameter vacuum port with a soft rubber cap on it? usually in center rear of the baseplate. that cap can blow off, cause big idle problems. it need a hose clamp on it.

The big vacuum port at the back of the carb has the PCV valve hose hooked to it and is still intact. The only other two vacuum ports on the carb have rubber caps on them. If I hook a vauumc gauge up to it, how will I know if I have a leak? I am assuming the gauge would read zero? Any other ways to check for vac leaks? Is there anything internal in the carb that could gone bad? Any other suggestions on what to look for?

Thanks for the advice so far!

Well if the guage reads "0" you have a HUGE problem, or you are at wide open throttle. You should have a reading of some sort on the guage and we can't say what it is because it will be differant with differant cams, intakes and so on. One way to look for a vacuum leak is with carb cleaner, use it VERY sparingly and spray around the intake and carb area, listen for changes in engine speed. If you hear the engine speed up, you might have found a leak. Be very careful in the area of the distributer though, I don't want to hear that you blew up yourself or others. Good luck and please keep us up to date on what is going on.

go back to the basics, check the timimg, the dist could have been slightly loose and the heating and cooling of the intake could have let it slip. and what one are you using to trigger the box?
most vaccum leaks you can hear, if your exhaust is at a decent level that is.
if it runs,out of gear, at a very high rpm might be the idle circuit but i don't think so coming on after a 10 mile trip like that.
did it kick back at all when you went to start it?

Hmmm, was it kind of doing that from the begining? Because I just thought I share my experiences in mis-adjusting the valves (hydraulic lifters). I was too tight and it did not idle too good in the low and nether did on the top. It was after freshly started after a rebuilt, and did the break in first at about 2000rpm for 20~30min, then only discovered it when I lowered the idle after.. Ran excellent after proper adjustment.

Kazu

The problem seems to have gotten somewhat worse. When it first started acting up yesterday it was still idling ok but now it wont even stay running in park if the idle is below 1500. I replaced the PCV hose thinking it could be cracked and leaking vacumm but that made no difference. I also tried spraying some card cleaner around the base of the carb and all along the intake sealing area, I didnt hear any change in rpm. I also hooked up a vacuum gauge to the port on the carb baseplate and got a reading of about 10-15, it was fluctuating somewhat. This was with the engine running at about 1500rpm. Also sometimes the rpm seems to fluctuate up and down maybe 200 rpm and then it will run steady and then fluctuate and so on. Does any of this make sense?

I thought about maybe replacing the carb base gaskets to see if that might be the source of a vacuum leak. Good idea or is that just wasting time and money? If I get a chance tonight I am going to verify the timing and make sure the distributor hasnt slipped.

Thanks for the advice so far and keep it coming!

Just a suggestion but get a heat shield for your holley comes with big mother thick gasket. Maybe your holley is leaking where the carb meets the manifold.
As a quick check you should notice a difference in sound when you close off the choke horn. If no change try applying the choke manually If it runs a bit better with choke on then its a major vacuum leak for sure. I have also seen Holley 3310s with a hole tapped in the throttle linkage side of carb between venturis.
If its there then it should have a countersunk plug with an allen screw head.This can be a source of a vacuum leak especially if its an older carb...

I played with the timing and it didnt seem to change anything. I do have a heat insulator then a gasket then a nitrous pate and then a gasket and then the carb... those gaskets have each been on and off the intake a couple times so I think I will replace them and see if it makes a difference. Also look the carb over when its off.

Do you have vacuum advance hooked up to the dist? If so try disconnecting and plugging the line. The vacuum may be dropping enough when you put it in gear (lower rpm) to lessen the vacuum advance in the dist and you get the snowball effect. Also if your mech advance springs are too light it can lessen the mech advance when you put it in gear.

All the advance is handled by the ignition timing computer, my distributor is locked out.

Mystery solved! I had a friend come over tonight to help. He suggested removing the carb, taking it apart, and inspecting it. We found some dirt/sand stuff in the bottom of the float bowls and on the walls of the float bowls there was some kind of white corrosion looking stuff. We sprayed carb cleaner thru all of the passages and blew everything out with compressed air, put it back together and its running great again!.. We think that during my 10 mile trip some of the corrosion broke loose from the walls of the float bowls and some of it must have plugged up some of the passages. He also helped me adjust the float levels and idle air screws and it idles better than ever. The lowest it has ever idled before was 900-1000, now it is at 700rpm and runs much smoother.

Thanks to all who offered advice!