Expert: Brad Sears - 5/18/2008

Question
QUESTION: Hi Brad, I asked a question back in March and you were quite helpful, thanks again. New issue, I rebuilt my stock single barrel carb on my 6 cyl 55 chevy (three times now) and fuel still seeps slightly from the gasket between the air horn and float bowl castings. I thought that the seat and needle was the culprit (I've changed it now 3 times) but now am looking for other possible causes. The float is adjusted correctly. The car starts and runs great, it just leaks slightly. Could it be fuel pump (stock pump) pressure forcing its way past the needle and seat? I thought that the fuel wouldn't even get that high in the carb if the needle and seat were functioning properly. The gasket appears to be evenly crushed so I don't think the castings are warped. Any ideas? Thanks, Bob

ANSWER: Good morning Bob:
Well the reality of the fact is that the Rochester single barrel carburetor of that vintage seeped right from the get go new. Well gasoline was leaded and dyed bright red the results were butt ugly. The fuel level was so close to the top edge of the float bowl that the vibrations and jounces of driving splashed the fuel around pretty good. The theory was at that time that the gasket material would then get soaked an wick the fuel to the outside, enough to stain the outside of the float bowl. During the 50's I was the carburetor and tune up guy in our families garage business. Lived through that period. So, the question that you ask is why engine oil does not wick the same by the engine gaskets? Simple, oil is more viscous. Thanks for the note and glad that this is the only problem that you have.
Brad

---------- FOLLOW-UP ----------

QUESTION: Thanks for your response Brad, So I take it that there is no cure and you would not apply a bead of gasket sealer to that gasket? Also, I was concerned that being right above the exhaust manifold and exhaust pipe there would be a fire concern however I checked with my chemist son and he told me that the self ignition, without a spark, temperature of gasoline was quite high. So I guess that isn't a concern either. Do you concur with that? Then from what you say it's merely an appearance thing? Bob

Answer
Good morning Bob:
The temperature of ignition of gasoline is above 700 degrees F so fire is out unless there is a lot of gasoline spilling on the hot manifold then making enough fumes to travel to the distributor and then ignited by the spark at the points. No gasket sealer at the float bowl or any part of the carburetor please. Good luck.
Brad