The Stovebolt Site Forums The Shop Area Engine Shop Carb insulator gasket question.

when I got my Offy 2x1 and insulators, they only came with one gasket. I called Patricks and they advised me to only run a gasket between insulator and carb, what do you guys think? Im afraid of an air leak between the manifold and insulator.

I am under the impression that it is the correct way to do it. I only have the one under the carb.

What is the face of the insulator made from....fiber? If so you shouldn't need another gasket. If it is hard phenolic or such, you would need a gasket. Some spacers had gasket facings on both sides.

It's a hard phenolic spacer.

It needs a gasket on both sides then.

On my 49 216 I only have 1 gasket between the Rochester B carb and insulator and no gasket between the insulator and manifold.
Thats the way it was when I disassembled the topend. I thought it odd that it didn't have a gasket between the insulator and manifold but since the kit didn't include 2 gaskets I reassembled it the way I found it.
Works great w/no vacuum leaks.

Does anyone know where I can get a thin carb gasket? I had to pull the studs up just to fit this gasket and insulator, I'm not sure how much more stud I have left.

Make your own out of cardboard or manila paper. Or, simply use a gasket sealer (without a gasket) under the insulators.

Stock intake manifold is cast iron.
Insulator face mating against intake manifold is phenolic.

Carburetor base is cast iron (at least with the W-1).
Insulator face mating against carburetor is phenolic.

Same type of interface. Same materials. What reason is there for one interface to use a gasket and the other not?

Any parts store should stock either small sheets or large rolls of gasket materials. You want a fiber sheet (vegetable or cellulose) with a nitrile or butyl binder. Comes in thicknesses down to 1/64".

The factory assembly manual doesn't show a gasket at all, just the spacer.

The factory spacer would have had fiber facings on it. Nobody used a phenolic spacer with no facings for a carb mounting. OEM phenolic spacers were made with the facings bonded on. The aftermarket sells lots of spacers of phenolic that have no facings, and in this case, they probably assumed you had the original gasket, and therefore supplied only one.

I have been working on 216 and 235's regularly for 50 years and I have never seen any kind of bonded facing or a gasket between the spacer and the manifold on a unmolested engine.

Pre '68, Phenolic or fiber spacers? A lot of the spacers were fiber core with laminated facings, and the whole thing encapsulated in a nitrile coating.

Thanks, Dave,

I've only been playing with these engines for about 45 years, but not professionally, like you.

I also do not recall needing a gasket under any type of spacer, unless the intake manifold was pitted?

Good thread.

Question, is the bottom of the phenolic cast smooth, or is it cored out or embossed?

Yes the bottom is cast smooth.

Interesting. I'm wondering if it gets too hot for the fiber material.

This area is very easy to check for vacuum leaks with an UNLIT propane torch. Mount it without the not-called-for gasket and test for leaks. BTW, ALL carbs have some vacuum leaks. Otherwise you would not be able to move the throttle valve shafts. It is the major vacuum leaks that cause trouble.
Carl

So I was dragged away from my computer last night. First, it is obvious that the lower gasket is not needed on these engines. I am thinking that any slight leakage would not be noticed, as you would cover it up when you adjust the idle mixture. These are pre-emission engines.

In the mid 60's emissions became the concern. Carbs were made as lean as possible. Evaporative emissions were an issue. Not only could you not have leaks from an unsealed joint, you could not even have leaks from the permeability of some of the gasket materials. The fuel system gaskets were encapsulated to seal the surfaces and cut edges. This led to problems from sticking the flanges together, so a release coat was added over the encapsulant. Materials such as mica or Teflon were used. Teflon was easy to add dyes to, so various packagers and distributors wanted their products color coded. That's how we ended with Holley float bowl gaskets being blue, while others chose green or red, as can be seen in performance parts catalogs today.

In 1968 VW introduced the Kammbach station wagon with EFI, and that was the first nail in the coffin for carburetors and the emissions problems they caused.

I'm on the side of Dave and Tim, never saw one with a
facing on it, and I sold them back in the 50's-60's
as a Chevy parts man. The original insulator was a
similar to a Phenolic 'Laminate' which had a slight
amount of give to it. They probably used a cotton
filler or possibly asbestos so that it had enough
give that when it was sandwiched between the two
machined surfaces of the cast iron carburetor and
cast iron manifold, it would conform to the very
small imperfections on the surfaces.
The reproduction ones sold by the vendors today as a
replacement appear to be phenolic also because it
can take the heat, but they just use a filler such
as carbon black or clay in the compound and are not
a laminated part. This makes them hard like the old
phenolic (Bakelite) radio cases and electrical
components are made from. Because of the material
that the new insulators are made from, I use a
standard gasket both on the top and the bottom. I
personally feel that for proper operation, there
should be no vacuum leaks where the fuel/air mixture
is concerned.

Denny Graham
Sandwich, IL

Yeah, the Bakelite type black phenolic material is what I was referring to. It's just a molded part. That's why I was surprised that they didn't use a gasket. All the ones we manufactured in later years for OEM and aftermarket had bonded facings. We purchased the phenolic cores from various vendors.