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Coleman396 06-04-2003 08:17 PM

Poor Idle- Low Vacuum
Hi Guys. I could sure use some input here.
First off I am just getting my 55 Chevy truck together and have a bit of a problem with the engine.
It is a rebuilt 327 with 462 heads,comp 274 cam performer intake and a 600 Edelbrock carb. Cam specs are as follows,Duration at .06 is 274-286.Lift is 480 int. 490 exhaust.
Now the idle when turned down sounds Healthy with a good lope to it. The problem is it seems to run fairly well with the idle turned up to maybe 1000 rpm but under that it seems to to fluctuate to the point where it slows down so much it will stall while just sitting there. Vacuum gauge reads about 5" at idle. Is this a carb problem? Distibutor?
Anyone got a guess what might make it so inconsistant at a reasonable idle speed? I know someone else using the same cam and his runs and sounds great at idle. Any hints would be greatly appreciated.
Oh yes,I do have a new 750 holley but had hoped to find out what the problem is before switching carbs. Thanks a lot....

72elcamino 06-04-2003 09:52 PM

I'll be interested to see some responses on this I posted a similar question a while back. I'm not to good with my cam math so I'm not quite sure how much cam that is, but it does seem like you might have a vacuum leak or possibly the cam installed wrong. Is the idle problem in gear?

MHenricks 06-05-2003 05:39 AM

I wouldn't change carbs. Check for vacuum leak at the manifold. Do you have good compression, you might have a valve not closing completely. What brand of intake gaskets are you using? I used SCA brand aftermarket and they came aprt after about 700 miles and caused a really bad vacuum leak. Is your carb new or used? make sure the base gasket is good and the base plate of the carb straight. What kind of base gasket are you using? If you have a thin gasket try a thicker one from like what GM uses.

That should keep you busy for awhile. Good luck

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