Hey guys,
I am helping my neighbor find a vacuum leak on his '67 Camaro 327. It had the original dual jet on it that he just replaced with an Edelbrock 4bbl intake manifold and carburetor, and now he has a serious vacuum leak. He put an EGR manifold on it and used the plug that came with the manifold to plug off the EGR passage. My question is can it leak vacuum at the EGR plug, located on the right side of the manifold, just below the carburetor?

Thanks guys,
Andy

Sure. One passage could leak exhaust gas OUT, the other could leak air (or some of that exhaust gas) back INTO the air/fuel mixture in the plenum.

Happens all the time with cheap, thin block-off plates that don't properly seal the gasket to the manifold.

Do remember that that isn't the only place you could have a vacuum leak. Did you have to remove the big oil separator canister in the lifter valley to get the manifold to sit on the heads properly? Years ago, I tried to put an aftermarket manifold on a '66 small block; the canister wouldn't let the manifold drop onto the heads at the back.

My neighbor's Edelbrock intake only has 1 large exhaust passage. The block off plate is located just below the carburetor on the right side of the intake manifold. If I took the plate off, would it have vacuum or emit exhaust? I've tried 2 different gaskets with that block off plate and have also tried silicone, which made no difference so far as the vacuum leak is concerned. Are the EGR block off plates that come with the Edelbrock intake manifolds usually good enough to seal off the passage? Yeah, I'm not sure about the canister. I wasn't there when he installed the new intake. He's just consulting me about the vacuum leak he's having.

My neighbor's Edelbrock intake only has 1 large exhaust passage.
Unlikely. Got a photo?

The block off plate is located just below the carburetor on the right side of the intake manifold.
Yup, sounds like the EGR location.

If I took the plate off, would it have vacuum or emit exhaust?
That answer would be..."Yes". It will blow exhaust out of the passage that supplies exhaust to the inlet of the EGR valve; and it will have vacuum from the port leading to the EGR outlet. When the EGR valve is in place, it connects those two passages, so the exhaust is routed to the plenum of the manifold--or--the pintle of the EGR valve plugs one opening, preventing the exhaust gas from getting into the plenum.

You better scrape the carbon off and see if one or the other of those two passages is hidden or partially plugged. That'd be pretty common.

Either way, you need a real live EGR gasket--NOT silicone--and the best blockoff plate there is, is a genuine EGR valve that doesn't have a vacuum hose attached. Nothin' better than that heavy cast-iron base to properly compress the gasket.

If there's only one hole it's probably not EGR and not a vacuum leak. Just a plain old exhaust heat crossover. Look again.

What carb is on it? Some Edelbrock manifolds need a thin steel plate with gaskets over and under to seal vacuum leaks right in front of the rear carb bolts.

Can tou come up with the model numbers of the manifold and carb?