An Experiment
Joe,
I think a test is in order here if someone with an AFB carburetor is willing to participate. If one of these cars was run to op temp and then immediately remove the carburetor, we may learn where the fuel is going. I've done this many times in the 60's and early 70's when Rochester had the same problem with their Q-Jet. Secure a long tapered punch vertically in a vise and place the carburetor on the punch through one of the mounting holes. You will then be able to view any dripping that may occur, if that's what the problem is.
I have a feeling there will be no fuel dripping from most of these AFB's. I think the problem is evaporation. I remember this exact problem from when these cars were new but it wasn't as severe as it's been in the last 20 years. The one thing that has had quite an effect on the speed at which the evaporation occurs is the difference in the fuel that we've had since the late 70's.
When the engine is shut off at op temp, I believe most of the evaporation occurs in the first 45 minutes, but not enough to prevent the car from starting the next day. From there, the rate of evaporation slows down but eventually takes the remaining fuel in the bowl causing the exact problem everyone has described.
This problem is not unique to Corvette or even old cars. I still have my 85 S-10 Blazer (yea, I know, time to get rid of it) with a carburetor and it does the exact same thing that everyone here has described. I've gone through the carburetor several times over the years but the problem continues. There's zero leakage from the float bowl and no leak externally. It's just an evaporation problem. If I run the engine for just a minute or two to shuffle cars in the driveway, it takes several more days for the fuel to evaporate but if I shut it off at operating temp, the bowl is empty in about three days. Will be interesting to hear any results of the test, especially if done with a hot carburetor.
Michael
Joe,
I think a test is in order here if someone with an AFB carburetor is willing to participate. If one of these cars was run to op temp and then immediately remove the carburetor, we may learn where the fuel is going. I've done this many times in the 60's and early 70's when Rochester had the same problem with their Q-Jet. Secure a long tapered punch vertically in a vise and place the carburetor on the punch through one of the mounting holes. You will then be able to view any dripping that may occur, if that's what the problem is.
I have a feeling there will be no fuel dripping from most of these AFB's. I think the problem is evaporation. I remember this exact problem from when these cars were new but it wasn't as severe as it's been in the last 20 years. The one thing that has had quite an effect on the speed at which the evaporation occurs is the difference in the fuel that we've had since the late 70's.
When the engine is shut off at op temp, I believe most of the evaporation occurs in the first 45 minutes, but not enough to prevent the car from starting the next day. From there, the rate of evaporation slows down but eventually takes the remaining fuel in the bowl causing the exact problem everyone has described.
This problem is not unique to Corvette or even old cars. I still have my 85 S-10 Blazer (yea, I know, time to get rid of it) with a carburetor and it does the exact same thing that everyone here has described. I've gone through the carburetor several times over the years but the problem continues. There's zero leakage from the float bowl and no leak externally. It's just an evaporation problem. If I run the engine for just a minute or two to shuffle cars in the driveway, it takes several more days for the fuel to evaporate but if I shut it off at operating temp, the bowl is empty in about three days. Will be interesting to hear any results of the test, especially if done with a hot carburetor.
Michael
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