1967 Holley 3811 manifold gasket/shim

[Owen L.]

My '67 427/390 has a replacement (repro) Holley that I got about 10 years ago. It came with a steel 4-hole shim that I used between the carb and the manifold gasket, which is a 4-hole gasket with the crossover slot.

Is there any kind of gasket used between the flat steel and the carb? When I took my carb off to check idle slot and secondary presetting, there was evidence of fuel seeping between them. I assume if fuel is seeping, then air is also traveling in the opposite direction.

Thanks for any info on my question or how to install the carb to eliminate the seeping.

[Vernon S.]

[Stephen L.]

Re: 1967 Holley 3811 manifold gasket/shim

There is a gasket on the manifold with a metal baffle on top and then the carb mounted on that. 67 427/390 w/3811 Holley carb.

Check your AIM

[Owen L.]

Re: 1967 Holley 3811 manifold gasket/shim

Thank you Skip and Stephen.

So it sounds like my parts and installation are correct:
Holley.jpg

[Joe L.]

Re: 1967 Holley 3811 manifold gasket/shim

Thank you Skip and Stephen.

So it sounds like my parts and installation are correct:
[ATTACH=CONFIG]100459[/ATTACH]

Owen------


Yes, the shield is there to prevent direct exhaust heat from the "heat slot" from directly contacting the carburetor. If this were to occur, the carburetor would be destroyed in short order.

The best plan is to plug the holes on either end of the "heat slot" thereby eliminating its functionality. Even with the shield the "heat slot" still causes a lot of carburetor problems and is best eliminated. After elimination, the shield would not actually be necessary but it won't harm anything to leave it installed.

GM eliminated the "heat slot" after 1969. Good riddance.

[Owen L.]

Re: 1967 Holley 3811 manifold gasket/shim

The best plan is to plug the holes on either end of the "heat slot" thereby eliminating its functionality. Even with the shield the "heat slot" still causes a lot of carburetor problems and is best eliminated. After elimination, the shield would not actually be necessary but it won't harm anything to leave it installed.

Joe,
What is the procedure to plug the holes? Does the manifold need to be pulled to do it?

[Joe L.]

Re: 1967 Holley 3811 manifold gasket/shim

Joe,
What is the procedure to plug the holes? Does the manifold need to be pulled to do it?

Owen------


The holes can be plugged in either of two ways. First, drive plugs (cup shaped plugs like small freeze plugs) can be installed. These are simply driven into the holes. There is no need to remove the manifold. I do not recall the size but simply measure the diameter of the holes and use the appropriate size.

Another method is to drill and tap the holes for internal hex drive NPT plugs. If the manifold is on the engine one needs to exercise care to catch and remove the metal chips. This is not too difficult. However, keep in mind that any chips that are missed will not enter the engine, only the exhaust system. They should not do any real harm here.

[Owen L.]

Re: 1967 Holley 3811 manifold gasket/shim

Thank you Joe. Both methods sound quite doable and it's good to hear the manifold can stay on the engine. Perhaps the next time I need to pull the carb I'll tackle it.

[Tom D.]

Re: 1967 Holley 3811 manifold gasket/shim

We are dealing with issues on a '67 this week. Plugging of the "cold enrichment" feature (if I have the words right).
gasket & Plate - 1.jpg

[Owen L.]

Re: 1967 Holley 3811 manifold gasket/shim

We are dealing with issues on a '67 this week. Plugging of the "cold enrichment" feature (if I have the words right).

is the purpose of blocking the cold enrichment passage to help alleviate heat soak of the Holley?

[Joe L.]

Re: 1967 Holley 3811 manifold gasket/shim

is the purpose of blocking the cold enrichment passage to help alleviate heat soak of the Holley?

Owen------


That's one of the purposes. But, as far as I'm concerned, the main purpose is to prevent deterioration and distortion of the carburetor. Even with the shield, a lot of heat is transferred to the carburetor.

[Tom D.]

Re: 1967 Holley 3811 manifold gasket/shim

is the purpose of blocking the cold enrichment passage to help alleviate heat soak of the Holley?

I'm doing it (with plugs and the under-carb shield) to improve performance when the coolant gets to 200 degrees F.