This is a newly rebuilt motor. It's a 350 block stroked to 383. Iron eagle heads, weind dual plane manifold, 750 cfm holley w/ vacuum secondaries, 282HR comp cam, and aftermarket HEI distributor.

The timing seems to be right, we are able to get it to run for a little bit at 1000 rpm and it's around 10 btdc and when it revs to 3000 rpm it's somewhere between 30 and 40. And we've moved the distributor back and forth slowly and it seems to like it where we have it. We've gone over the rocker arm adjustments a couple of times.

We cannot get it to idle and just the slightest opening of the throttle plate and it revs way up and holds there for a few seconds. To keep it running you have to tap the throttle every few seconds.

I think it seems like a vacuum leak. Problem is there are not many visible places for a leak to exist on this motor. The holley only has three ports. The big one for the brakes, the ported one for the vacuum advance and the open one we are using on the mallory fuel pressure regulator. But we have even tried running it with all three plugged. And the manifold only has one vacuum port that is plugged. And fuel pressure is steady at around 5 to 6 psi.

The manifold looks like it is sealed up good to the heads. Is there any where else internally to have a vacuum leak. Or does the revving up even when the plates are closed sound like something else.

Sorry so long. Again the engine revs way up with the slightest opening of the plates and won't idle without tapping the throttle every few seconds. Additionally the power valve has been replaced in the carb and the cam was not degreed in, just lined up dot on dot.

 

ttt one more try

 

well i'm not carb guy but have you played with your mixture? maybe you need to step up to a slightly larger jets? you running lean?

TTT

 

Thanks for the response mystikkal. It does not seem to be running lean. We can keep it running by lightly revving it for quite a while and it runs real cool. Headers don't glow or anything.

And as far as getting it to idle I believe with holleys the mixture screws determine the leaness or richness at idle. Probably like that with all carbs really. But adjusting the mixture screws has not been changing much at all, which is another reason I think we have a vacuum issue somewhere.

 

Sounds to me like it's WAY WAY lean at idle, which of course would be consistent with a vacuum leak.

But it can also be an internal carb problem. Try a different carb. Or, if you're familiar with Holleys, tear it down and make sure it has the right gaskets and that they're not upside-down or anything.

 

I'm actually much more familiar with Q-jets. And that was my next step. I know you can use an adapter to put a holley on a q-jet manifold, but not sure if I can go the opposite way with my q-jet on his holley type manifold. I would think it would work just to see if we could get it to idle using the primaries only and either rule out the carb being the issue or finding out it is the issue.

I may take the holley apart anyway and get a better look. After replacing the power valve it looks pretty simple.

Thanks

 

update, this should go under what not to do when working on your car.

I pulled the holley off and the gasket was burnt. There where a few backfires while we where trying to get it to run right but the gasket should have not been affected since it is pressed between the carb base and the manifold. Then upon removing the gasket there are washers around the studs. Somehow between the three people putting the motor together washers where left on the studs before the carb was put on. Making a nice little gap all the way around the carb base. And it was hard to visibly see that.

Anyway if fired right up once the offending washers where removed and idles great. Kind of funny huh.

 

i may have read this whole thing wrong, but i know vacuum leaks can make it rev up when the blades are closed even :lala:

 

Did u mean to say can't rev up? If so, let me explain. When the throttle was opened it would rev up and upon closing it, it would rev a little higher and finally die down after a few seconds. You see it still had enough fuel from the squirters and idle circuit to supply the air coming in from the base of the carb where it was not all the way sealed to the manifold. The accelerator pump was the only way to make it come anywhere near idleing cause the motor was getting air from around the base of the carb along with the throttle plates.

You should try it sometime.

 

yeah making sure no vacuum leaks are present, especially on a carb, is critical. good vacuum, with no leaks, is required for a the carbs' verturi effect to meter fuel properly. i'm glad the problem was an easy fix. have fun tuning.