The Stovebolt Site Forums The Shop Area Engine Shop Carb Insu;ator Question

My rebuilt Rochester came back with a new gasket. Does it fit between the bottom of the carb and the black insulator or between the insulator and the intake manifold. I do not remember if the old setup even had one at all. Thanks Ralph

Ralph,

I believe the factory configuration was the phenolic block set directly on the manifold and the gasket was sandwiched between the top of the block and the carburetor base. Lots of folks run this every which way, but the important note is the location of the small notch in the base gasket. It must coincide with the small vacuum hole in the carb base.

Stuart

Thanks Stuart. I looked at the vacuum hole and the block..... wonder where does it pull the vacuum from as the block does not have a hole that matches the carb base? I see the gasket allows for the hole in the carb but the p-block is solid? I think placing the gasket under the carb also makes the most sense. Ralph

Ralph,

If you sandwich the gasket betwixt the insulator and carb base, the vacuum path is through the skinny space developed by the thickness of the gasket itself. The little notch keeps this path open to the bore of the intake. I think this is how it works.

To be honest, I never have understood why the fit of the insulator to manifold is OK without a gasket but the fit of insulator to carb base needs a gasket..makes no sense to me, but I'm just a dumb Millwright.

Stuart

You should have a gasket above and below the block. I don't know what Chevy had originally on your '58. Chevy used a block under the Rochesters on the Corvairs with gaskets above and below on both carbs. The later engines with four Rochesters used a total of eight gaskets and four blocks.
Even if you don't have a leak by not using two gaskets, you may crack the phenolic block. You will have a real leak then.

Where do I locate the correct gasket to mate up to the P-block. I will put one between the intake and block if I can find one. I guess it would be the same as the carb base, but I do not want to get a whole rebuild kit just to get the correct gasket. Thanks Ralph

Just get a piece of sheet gasket from your local parts store, they can tell you which type to use. Then use the existing gasket as a pattern and cut it. Slots for vacuum are not necessary on the gasket that goes between the manifold and spacer. Incidentally, my spacer has a 1/8" deep notch in it were it meets the carb vacuum hole.

You can get gaskets at NAPA. The last time I bought some they came in pairs. one for under the spacer and one for under the carb.

My spacers also had the cutout for the vacuum hole. It would be easy to add one if you wanted to.