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Old 06-11-2007, 08:46 PM
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internal vacuum leak in sbc????

I was wondering, does anyone know the symptoms of an internal vacuum leak?

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Old 06-11-2007, 08:52 PM
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One symptom is oil consumption, comes in from the lifter valley and gets sucked into the intake ports. Spark plugs will be really carboned up. Aaron
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Old 06-11-2007, 08:54 PM
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Check this out.
http://www.therangerstation.com/Maga...acuumLeaks.htm
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Old 06-11-2007, 09:11 PM
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reply internal vacuum leak

I have seen oil on the plugs lately and adding oil more frequently. Also when the car starts cold, it runs fine nice thumpity cam rumble. But after I drive it for a little while I notice the car seems to idle alot higher and it sounds like a normal V8, no thumpity cam sound anymore I checked everything externally to see or hear any vacuum leaks with a little carb cleaner,nothing. So Im thinking it must be internal. Anyone else ever had the same problem?
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Old 06-11-2007, 09:44 PM
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Pull the carb and look in the plunum, if you see oil everywhere, you have a leak.
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Old 06-12-2007, 06:50 AM
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if you put a vacuum gauge on it starting from when it is cold, what is the cold reading and does it slowly go down as the engine warms.
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Old 06-12-2007, 07:00 AM
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Is the carb a quardrajet??

I've worked on a few of those that had internal vacuum leaks inside the carb. New carb kit & inspecting everything did not help. Last one was a 72 Vette and ended up with a remanufactured carb from a chain store and it runs mint.

That one sounded like a modified cam, and was hard to get the cold & hot idle correct.

I've talked with a few others and they have seen the same problem; something about warping inside the carb.

I also have seen intake gaskets go bad on a very few SBC.

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Old 06-12-2007, 07:38 AM
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Quote:
Originally Posted by Danscam
I have seen oil on the plugs lately and adding oil more frequently. Also when the car starts cold, it runs fine nice thumpity cam rumble. But after I drive it for a little while I notice the car seems to idle alot higher and it sounds like a normal V8, no thumpity cam sound anymore I checked everything externally to see or hear any vacuum leaks with a little carb cleaner,nothing. So Im thinking it must be internal. Anyone else ever had the same problem?
Yep, except mine doesn't have a "thumpity" cam. Vacuum reading was steady but low, oil consumption a Qt. every 50 miles, a light blue haze when I accelerated and oil fouling the plugs within 200 miles. Intake gaskets were leaking. A previous owner had installed an aluminum intake and used cheap gaskets plus didn't get the heads clean of the old gasket. Replaced those, cleaned the mating surfaces REALLY well and oil consumption dropped to barely measurable, vacuum came up to within factory specs and no more haze following me around. Almost 2,000 miles and haven't had to add any oil or change spark plugs. Not too bad for a 31 year old car with the original long block.
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Old 06-14-2007, 08:54 PM
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vac leak

I have a 650 holley dp about 6 months old so I dont think its the carb. I just noticed the idle increasing, idles at 750-800 rpm but after driving for a little while it jumps to 1000-1100 rpm which I think is a little high , also I noticed oil on the plugs. Guess Ill work on it this weekend to see if I can figure out this problem. Im wondering I have a set of trick flow heads on the car and rpm performer intake, dont know if they match up too well "port holes". does anyone else have the same set up?

Last edited by Danscam; 06-14-2007 at 09:00 PM.
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Old 06-16-2007, 10:29 PM
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I have TF 23* heads and a Performer RPM Q-Jet on my '76 'vette. Heads and intake both matched up well with FelPro 1205 (the recommended) gaskets.

I am going to pull the intake, oil leak at the rear, to check intake sealing, as the block has been '0' decked, which amounts to at least 0.025. Intake bolts did align correctly.
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