HEAT INSULATORS (commonly referred to as spacers)
I had not previously posted an answer to this question, as sufficient information was not given in the question. Buckaroo has now sent an email with more information.
This answer applies specifically to 1953 - 1958 Chevrolet trucks with 235 CID engine and Rochester 7004468 carburetor.
As ORIGINALLY BUILT, the truck came with a spacer between the carburetor and the intake. NO ADDITIONAL GASKETS WERE USED. The spacer is 0.610 inches thick. The insulator was installed with the slots toward the carburetor.
The following applies in general to most early carburetor spacers.
The spacers are made from asbestos fiber. Due to the discovery that asbestos was not particularly good for humans, asbestos fiber spacers were phased out. New old stock spacers bring what many would consider to be ridiculous dollars from those doing 'show' vehicles. The carburetor kit manufacturers (including Rochester) started including one thin gasket with the repair kits on the theory that one would remove the carburetor, but not the spacer (or to cut down on the cost of the kit), and the thin gasket was used on top of the spacer. Today, most enthusiasts either build up the thickness of the spacer by ganging together a sufficient number of flange gaskets; or machine a spacer from hardwood, and place flange gaskets on either side. As the correct flange gaskets are slotted, one need not machine the slot in the wooden spacer. Other enthusiasts have machined spacers from aluminum. These may work, but due to the thermal conduction properties of aluminum, may contribute to idle issues in very warm climates.
Please understand that Rochester made HUNDREDS of different type B carburetors. NO GENERAL ANSWER CAN BE ASSUMED TO BE CORRECT FOR ALL APPLICATIONS. ONE MUST KNOW THE EXACT APPLICATION AND CARBURETOR IDENTIFICATION NUMBER TO BE SURE!
Jon.
