Greetings, After loooking at tons of pics of dual intakes on 216/235/261s, ive noticed that some set ups have carburetor insulators, and some dont. What are the reasons to run one way or the other. Designed to work that way?.... Climate?..... Make of carb?.... Leeekchester/carter/stromberg Brand of intake?... It loooks better?.... Thats how dad did it?... Thanks, 009
In my opinion, the insulators are key to keeping cool carbs and hot intake for best fuel atomization.
The function of the insulator was to stop vapor lock, or at least help it. I don't run them on mine only because I only had one when I put the duals on. With "B" Rochesters. The manifold gets really hot. But I never had a vapor lock problem either. And last summer I was down in NC with it and it reached 105 outside air temps. So I guess it's a non issue.
Another of the questions for which there is no definate answer, as each installation will be different. It is quite possible that some of the "spacers" you have seen are actually "adapters"; either to rotate the carburetors 90 degrees on the intake, or to allow a size 3 carb on a size 2 manifold or vise versa. Use of the spacer MIGHT, depending on a lot of other variables: Increase marginally high RPM power. Decrease marginally low RPM driveability. Help minimize vapor lock (not generally an issue with inline engines). Contribute to carburetor icing (much more of an issue with inline engines). Make linkage easier. Make linkage more complicated. Create hood clearance issues. They are not very expensive, try with/without to see which way YOU prefer. Personally, I would NOT use them with an automatic transmission; and probably would not use with a stick, but I WOULD try both ways. Jon.
If i remember correctly, there's a port on the bottom of Rochesters that require you to use the Insulator, but that's only if my memory still works
You can run rochesters without if you use the sloted base gaskets . I would run the phenolic spacers if possible, they help warm weather driveability greatly.
I'll add my experiences with and without. With a 54 235, Tattersfield intake and two one barrel Carters I had vapor lock problems when I had no spacers. After I put them on I had no more problems. You may want to be sure you heat your intake also if it isn't already. Dom
You should try both ways to find out what works best for you. I've only used the bakelite insulator when I ran the single cast iron intake/exhaust manifold, like stock. On the cast aluminum dual intakes with exhaust heating (tubes and direct header bolt on), I never used the insulators and never had any problems in all the years of daily use, including annual triple digit summers, hours long desert freeway trips and starting after parking during those trips and sometimes 200º coolant temp on my trusted 235. In other words, never had vapor lock, or poor mileage or power. I always assumed the insulator is not required with cast aluminum intakes like with iron.
Just as PBRmeASP and Unsafe6 said, you need to have a path for vacuum to the small, approx. 1/8 dia. vacuum port in the bottom of the carb. If you cover it with the gasket, you won't have a working idle-circuit, and of course, your engine won't idle. The carb-spacer has a fairly deep slot for this purpose. Using just a thin gasket increases your chances of the port being closed off by debris, or by gasket-sealer if you happen to use some. For that reason alone, in addition to the other reasons given, I would use the spacer if you can.
Good advice for Rochester Bs and other carbs with passages drilled into the flange surface. You can use the thicker old style gaskets or modern thin ones with the insulator.
thanks.... The second Pileup i had carb problems due the that vacume port on the bottom of a BC carb, wouldn't idle worth a damn....
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