I am cleaning up the carb mounting surface on a '64 intake (#3844459). Standing on the side of the car and looking down, there are six holes. The two on the right and left are threaded and mount the carb. There is a third set of two, however, in the mounting surface, about inbetween the 4 intake holes. On my intake, one is full of carbon gunk, the other has been filled with some kind of epoxy. The gaskets I have are solid and would cover over these holes. Can someone tell me what they are for?
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Re: C2 intake - extra holes on carb mounting surfa
Mark-----
The holes that you are referring to are for the infamous "carb pre-heat" system used on many mid to late 60s Chevrolet V-8 engines. These holes are designed to provide exhaust crossover heat to the carb base in order to heat it and better atomize fuel, especially during cold engine warm-up. The holes were designed to be used as part of a "system" which also included a grooved, insulator-type gasket and a thin stainless steel heat shield. Although some engines also used a groove in the manifold between the holes, your particular manifold did not. It used just the groove in the gasket to provide a passage for the exhaust gasses. When the "pre-heat" system is operational, it's VERY important that the gasket and the stainless steel shield be installed properly and as-designed. The gasket goes on top of the manifold and the stainless steel baffle goes on top of that, with the carb resting directly on the stainless steel baffle.
The big problem with this system is that the pre-heat ruins carburetors, especially throttle body and float bowl assemblies. It's just not worth it for the benefit conferred and Chevrolet completely abandoned the system for the 1970 model year and beyond. I always recommend that the system be permanently disabled. This can be done by drilling and tapping the 2 holes you described for allen head pipe plugs. This must be done with the manifold off the car, though. On the car, you can install cup-shaped soft plugs available from auto part stores. However, you CANNOT plug the holes with epoxy of any sort which MAY be what some earlier "klutz" tried to do if what you describe is actaully the case. Epoxy of any sort that you're likely to be able to get your hands on will absolutely NOT withstand the heat involved.In Appreciation of John Hinckley -
Re: C2 intake - extra holes on carb mounting surfa
interesting, thanks. The "epoxy," or whatever it is, has been in the intake for years I suspect. I've had the car for 5 and never had the carb off before now. I'll plug the other one up as you suggest and when i take the intake off when rebuilding the engine I'll drill and tap them for a permanent fix.
When I took the carb off, there was a gasket, the metal plate and then another, thinner gasket that the carb mounted on. Do you think I should duplicate that, or just go with the plugged holes, the first gasket and then the metal plate?
Thanks again.
MarkComment
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Re: C2 intake - extra holes on carb mounting surfa
Mark-----
Now that you mention it, I think that the 64 L-75 set-up was a 3 piece affair. There was the gasket which went to the manifold, an insulator, and the stainless steel baffle. I think that I'd install all three just as they should be. Even when you get the holes permanently plugged, I'd still use the 3 pieces just as they were originally installed. With the holes plugged, you won't really need to use all of them, but they won't hurt anything, either. And, this way, your external configuration will be just as original. No one will ever know that the holes are plugged.In Appreciation of John HinckleyComment
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