BobE wrote:

I'd first try to isolate the leak, is it a vacuum leak or is fuel leaking out?
For a vacuum leak, try spraying water around the gasket with the engine idling and the RPM will vary when it sucks in the water.
Make sure you torque down the carbs bolts evenly in a criss-cross patten and check the torque that Edelbrock recommends.
Due to this issue, I'd use the Edelbrock recommended gasket.

 

I've already done as you suggested. The leak is definitely the carb gasket. Edelbrocks instruction say to use a short wrench and tighten in a criss-cross pattern. I did that and also re-torqued the manifold per their instructions. I noticed an improvement but it still cuts out under hard acceleration at 2000 rpm. I just can't get the carb gasket to seal. Don't want to over tighten and break something.

A gasket problem often shows up at idle.  If it is cutting out under acceleration, it seems more like a mixture issue or a problem with the secondaries.  If it runs normally under normal acceleration and cuts out when you hammer it, check float levels, mixture settings, etc.  You can also get this in some carbs when your carb is getting hot.  The primary circuit may function OK but when the secondaries open you can get some vapor-lock symptoms.  This may be more of a Holley problem rather than an E-brock problem.

What is your true idle vacuum (direct not ported)?  If it is normal and steady this would tend to indicate that you don't have a vacuum issue.  If your tests show a leaky gasket then it sounds like you have two problems.

Rather than a thicker gasket that may not compress fully/consistently I prefer a phenolic spacer (either open or 4-hole) with two normal carb gaskets.  The phenolic will provide solid support for the carb and it will tighten down consistently.  The phenolic spacer (1/2" or more depending on air cleaner clearance) also will provide better insulation and lower carb temps. 

I assume that this is a 600.  Some of the 750's were known for a serious lean stumble on acceleration.

Sounds like it may be two problems.  It sounds like some of the debris may have made its way into the fuel circuits.  Before you mount the carb, lay the gasket and/or spacer on the bottom of the carb and make sure there are no exposed passages and then verify the same on the manifold.  Look carefully at the studs on the manifold and make sure none of the four has any threads that have been pulled above the mounting surface.  This can prevent a gasket from seating.  When you open up the butterlies there is a lot more open area than a gasket leak so the gasket leak becomes very small by comparison.  How is your PCV valve?  Any issues with the valve or the hose?  A cracked hose will also respond to leak tests.

I prefer to use thin carb gaskets.  It keeps you from warping the carb base.  If you use a thick gasket, it is alot easier to overtighten one corner and warp or break the carb base.  It happens not when you tighten corner 1.  It is when you overtorque corner 1, then go tighten corners 2, 3, and 4 which applies alot of leverage to pull the carb down  into the softer gasket, then breaking or overcompressing corner 1.

Suggest checking the carb/intake manifold mating surface with a straight edge to determine if either is not warped.
I agree w/MS on the use of thin gaskets, but would also try doubling up on the gaskets, or use a thin coat of RTV to see if you can get the leak to stop.  Further actions to correct the problem can be determined from that point.

Ron68 wrote:

Does it cut out and miss and backfire, or does it just bog down then accelerate? The Edelbrock has different strength step up springs in a kit you can get. The springs are under the two small plates in the carburetor throat. Loosen the screws and swing the plates out of the way. Remove the step up pistons and metering rods and install a stiffer spring. This can cure the bogging down at heavy acceleration problem. Google changing Edlebrock step up springs. I had the bogging problem and went with the stiffest springs and no more bogging.

 
It's cutting out. Right at 2000 under hard acceleration. I doubt it's the springs because this is something new. Before that my little 289 was kicking some local small block Chevy butt.

Sometimes installing just one thin gasket will allow you to correct the warpage doen to the carb base caused by the thick gasket.  Install one thin one and tighten down the carb evenly and see what happens.  If you still think it is leaking, try squirting some starting ether sparingly around the base to see if the engine speeds up.  You have to keep the ether from entering the normal air flow of the carb or air cleaner, though or the test is voided.

MustangSteve wrote:

DO NOT use RTV on carb gaskets!  Sure way to  get all the vacuum passages in the carb plugged up, plus RTV is not fuel resistant.  Sorry, Bob, but gotta say that is not good.

 MS - no problem, I didn't think of the vacuum passages.  Personally, I've doubled, and tripled, up on carb gaskets to try to eliminate a vacuum leak ... finally had to fix the warp issue on the carb spacer.