Gasoline Smell - 1966 L79

[Joe L.]

Re: Gasoline Smell - 1966 L79

I have personally experienced what Joe Scafidi describes above, and I know other '67 owners that have experienced it. Today's fuels seem to have a lower boiling point than the fuels of the 1960s. If the car is parked with the engine hot, sometimes the heat soak causes the fuel in the fuel bowls to boil. Even if the fuel doesn't quite boil, the hot gas still throws of a lot of fumes.

While I think all Holley carbs have bowl vents that are open to the atmosphere (those two tubes that stick up into the air cleaner), the 1967 small block carb has an additional vent on the top surface of the front bowl. This vent is in the form of a rubber disk that sits over a hole in the top of the bowl. The carb linkage is arranged to open this vent whenever the throttle is in the idle position, such as when the car is parked.

I have no idea why Holley decided to add this feature in 1967, but they didn't use it for very long. Most Holley carbs do not not have this added vent. However, the combination of volatile gas and this open vent on the front bowl is a good recipe for gas odors, even if there are no actual leaks anywhere in the system.

I see that the OP lives in Texas where temperatures can get pretty hot. To reduce the heating of the gas in the carb, it helps to replace the heat riser valve with an open spacer, block the exhaust crossover path under the carb, and install a phenolic insulating spacer under the carb. This will probably keep fuel from boiling in the carb, but there will still be some emission of gas fumes after the car is parked hot.

Joe------


Holley used the primary float bowl vent you mention for the 1966-1967 model year 4 barrel carbs. They dropped it for 1968 4 barrels. Then, they brought it back for 1969-70 4 barrels. Even 1970 Holleys for EEC application (i.e California) had the vent. However, they were equipped with a strange contraption to capture the vented gasoline vapors. For 1971-72 the vent was gone again.

I've always wondered why they did this. Was the fuel bowl vent a good or bad thing?

[Timothy B.]

Re: Gasoline Smell - 1966 L79

My thinking is the vent is there to prevent vapor from entering the air horn from the primary vent stack and causing over rich mixtures. I have the vent on my 3810 Holley and have never had a problem with it, I can't remember it on any aftermarket carburetors.

[Joe R.]

Re: Gasoline Smell - 1966 L79

Joe------


Holley used the primary float bowl vent you mention for the 1966-1967 model year 4 barrel carbs. They dropped it for 1968 4 barrels. Then, they brought it back for 1969-70 4 barrels. Even 1970 Holleys for EEC application (i.e California) had the vent. However, they were equipped with a strange contraption to capture the vented gasoline vapors. For 1971-72 the vent was gone again.

I've always wondered why they did this. Was the fuel bowl vent a good or bad thing?

Hi Joe L:

I'm not sufficiently familiar with the internal construction of the Holley carb to determine what difference there is between the added external vent and the normal, tubular vent that exits inside the air cleaner. My impression is that the purpose of the tubular vent is to keep the air in the float bowl at atmospheric pressure.

An interesting aspect of the external vent is that it only opens when the throttle is at the idle position. So, whatever function it provides is only active when the engine is idling. As soon as the throttle is applied, even a little bit, the vent closes.

Of course, the vent remains open whenever the the car is parked with the engine off. That provides a convenient way for gas fumes to escape from the hot (possibly boiling) gas in the primary bowl.

[Leif A.]

Re: Gasoline Smell - 1966 L79

Ned,
So, the consensus of opinions is that you WILL have some gas odor after driving your car and you will notice it if you park your car immediately in the closed garage. We need to know from you if there is a strong gasoline smell the morning after you drive the car or has the smell dissipated?

[Edmund C.]

Re: Gasoline Smell - 1966 L79

Gentlemen: Thanks for all the responses. Most helpful and greatly appreciated. Best, Ned

[Patrick T.]

Re: Gasoline Smell - 1966 L79

I have a 30'x40' attached garage and after parking it, my (since sold) L-79 '67 Corvette after a drive, I never noticed any fumes of exhaust or gasoline. Then one morning I went into the garage and the whole place reeked of a gasoline. I immediately knew something was wrong. The first place I looked at was under the engine and there it was...a very slow drip of gasoline coming out of the engine where the fuel pump attaches.

Right away, I took a vise grips and crushed off the gas flow on the rubber fuel line. I had only replaced the "restored and rebuilt" fuel pump from the Goat Boy in L.A. a couple months before to make the car "numbers matching" for The Gettysburg Regional that my car was in. The Regional was now over anyway and I took out the faulty fuel pump and reinstalled the old pump I had before, back in the car. Problem over with. PT

[Joe L.]

Re: Gasoline Smell - 1966 L79

I have a 30'x40' attached garage and after parking it, my (since sold) L-79 '67 Corvette after a drive, I never noticed any fumes of exhaust or gasoline. Then one morning I went into the garage and the whole place reeked of a gasoline. I immediately knew something was wrong. The first place I looked at was under the engine and there it was...a very slow drip of gasoline coming out of the engine where the fuel pump attaches.

Right away, I took a vise grips and crushed off the gas flow on the rubber fuel line. I had only replaced the "restored and rebuilt" fuel pump from the Goat Boy in L.A. a couple months before to make the car "numbers matching" for The Gettysburg Regional that my car was in. The Regional was now over anyway and I took out the faulty fuel pump and reinstalled the old pump I had before, back in the car. Problem over with. PT

Patrick------

...just another example of why I've been advising against the use of rebuilt Unitac-type (crimped) fuel pumps for years.

Also, I'm amazed that you (and others) never experienced the odor of gasoline in the garage after parking the car and closing the garage door. I experienced it with my 1969 from the day it was new and continuing thereafter. The car had NO leaks, whatsoever, except for a few specific occasions of failures that were promptly corrected.

[Duke W.]

Re: Gasoline Smell - 1966 L79

My thinking is the vent is there to prevent vapor from entering the air horn from the primary vent stack and causing over rich mixtures. I have the vent on my 3810 Holley and have never had a problem with it, I can't remember it on any aftermarket carburetors.

That's a good reason. AFBs have a "hot idle compensator" - a bimetal thermostatic strip that opens at high temperature to expose a calibrated orifice between the two secondary throttle bores to draw in additional air in order to reduce an overly rich mixture that percolation can cause. When it opens idle speed should increase, but I can't recall ever noticing that on my 340 HP engine. I always wondered if that thing actually worked.

Duke

[Edmund C.]

Re: Gasoline Smell - 1966 L79

Gents: I took all your guidance into consideration and the issue now seems to be successfully resolved. After driving the Vette today, I opened the hood outside the garage and l let it sit for 20 minutes in the open air. When I ultimately put her away there was no noxious gas smell. Thanks fellows, as always, I appreciate the guidance. Best, Ned