Carburetor percolating?
Thread Starter
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Joined: Jul 2010
Posts: 1,835
Likes: 20
From: NC
Carburetor percolating?
I am thinking my Holley 4165 may be percolating, since I have seem some evidence of gas leaking by the secondaries on my newly painted manifold. When I look at the carb, the back side appears to be sweating. When I removed the carb to paint the manifold, there was a thin metal gasket with a couple other thin cardboard gaskets which I did not install when I put the carb back on. I had new flange gasket, and decided to only install that.
I want to put the thin metal gasket back on to see if it helps. Should it be in direct contact with the manifold or the carburetor?
I want to put the thin metal gasket back on to see if it helps. Should it be in direct contact with the manifold or the carburetor?
Last edited by binster; Jul 12, 2011 at 09:45 PM.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
When I ran a holley on the '77, it was obvious when it percolated. You could hear it in the front fuel bowl and gas shot out of the accelerator pump shooters after driving the car on hot days. Blocking the heat crossover and a carb. insulator stopped about 90% of it. I never got it to completely stop. The radiator was marginal also. mike...
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
IF your mani has a heat riser crossover, and you live south of say Minnesota....you need to block the crossover heat riser passage, and maybe install a electric choke....
I have fought that problem for decades, and in fact the only sure cure is to remove intake, clean it all up, and fill the crossover passages with Plaster of Paris.....
I have fought that problem for decades, and in fact the only sure cure is to remove intake, clean it all up, and fill the crossover passages with Plaster of Paris.....
Intermediate
Joined: Dec 2009
Posts: 32
Likes: 1
From: Snohomish Washington
You need an insulator...
When I swapped the quadrajet with the spreadbore on my 427, I purchased an insulator that was about 1/2 inch thick. I think it was from Mr. Gasket, but I can't remember, too long ago... It was comprised of several alternating layers of insulator gasket and aluminum sheet. It came with 4 layers (I think) but I used only three to keep the thickness down. Even at that, the air cleaner rubs the underside of the hood, and it will require bending a new linkage piece from the choke thermostat to the lever on the carb. I've never had any percolating issues, although I admit I live in Washington state and 90 degree days are few... By the way, do you have the fuel filter with the vapor return line??? Often times these are plugged off and replaced with a straight thru filter... If so, it could be contributing to your problem. The return fitting bleeds off boiled vapor between the pump and carb and recirculates the fuel in the line, generally keeping it cooler.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
IF your mani has a heat riser crossover, and you live south of say Minnesota....you need to block the crossover heat riser passage, and maybe install a electric choke....
I have fought that problem for decades, and in fact the only sure cure is to remove intake, clean it all up, and fill the crossover passages with Plaster of Paris.....
I have fought that problem for decades, and in fact the only sure cure is to remove intake, clean it all up, and fill the crossover passages with Plaster of Paris.....
Thread Starter
---------
Joined: Jul 2010
Posts: 1,835
Likes: 20
From: NC
Thanks all. Can I reuse the thin metal gasket that was on the car previously? Not sure if this problem was caused by me not using the metal gasket, or it s due to summer heat. I just got the car in feb, so this is my first summer with the car.
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Joined: Mar 2006
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From: Florida
Block off the xover first, method of you choice.
If you want to reuse your present shield, just use gaskets top and bottom.
Or you can use this larger metal type, works well with gaskets. This is from Holley
http://www.holley.com/108-70.asp
Or you can use other blocks as already mentioned.
If you want to reuse your present shield, just use gaskets top and bottom.
Or you can use this larger metal type, works well with gaskets. This is from Holley
http://www.holley.com/108-70.asp
Or you can use other blocks as already mentioned.
