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I guess I don't know much about carbs


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My '62 Skylark (215 V-8) started running rough when warm. If I manually close the choke, it runs great. So I take the carb apart looking for either a vacuum leak or fuel restriction. Well, I found a "vacuum leak". If you look at the pictures, you will see an intentional path to allow unmetered and unfiltered air into the carb above the throttle plates. I have a spare carb and unopened carb kit, and they are all the same. I've never seen this before. I guess I'll never hose down the engine...






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Interesting situation! If the design had been to have the "vent" under the throttle plates, then it would have been a vacuum tap for power brakes or similar . . . but as it's not threaded AND where it is, the hot idle "fix" make sense with respect to a "hot soak" situation.

Thanks for that link, Jon!


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I know we have been through this before, but your problems may be related to the available fuel (ethanol). Also my advice (that I don't always follow) is to be sure that your ignition system has no issues. When I put the 264 nailhead in my 51 F-1 I used the spark plugs that were in it --- Bosch platinum, right number and they looked new. Anyhow when hot it would idle roughly and was very hard to start. Finally after tearing the carb apart 3 times I checked one of the plugs on a lawn mower where it had a very thin barely perceptible spark...I then tried a used AC44 and the spark was splat,splat,splat....new plugs and it runs perfectly.

Also I noticed that your carb is probably a Rochester 4gc. One of our local chapter members had an engine fire in his 62 after one of the bowl plugs popped out (another effect of ethanol on the original cement). Also the current gas if left to dry in the carb leaves a white powdery residue. The 4gc on one of my 55's did not like that residue...I could clean it and it would run perfectly until the next time it dried out. That 4gc is in a box...the only carb that ever defeated me!


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