AkrHack

After a wild temperature swing here in the Midwest over the last couple days, there was a strong smell of gasoline in my garage. I suspected my 67 convertible which is stored on a 4 post lift since late November. When I walked under the car, I saw areas of the the engine block was wet with fuel. I just figured the fuel line was leaking where it screwed into the carb so I lowered the lift and opened the hood. I was shocked to see gasoline puddled (yes puddled) on top of the intake manifold. I pulled off the air cleaner and I could see that gasoline was seeping out of various places on the stock Holley 3810 carb. After seeing this mess, I immediately suspected the gas cap. When I removed it, there was a pronounced whoosh when the pressure was released. A prior owner replaced the gas tank and cap in 2012 (I have the receipts for both items from Zip that he gave me). I suspect that I now have gasoline in the crankcase that would have seeped in from the intake so the first order if business in the spring before I drive the car will give to change the oil.

Have any of the other members experienced this before? Do any if you have any recommendations where to buy a gas cap that actually functions how it is supposed to?

Thanks,
Rick

dkleather

Not sure if these are still available but worth checking.
https://www.corvetteforum.com/forums...-gas-caps.html
I bought a new one from CC and it was so bad I had to bend tabs to make it fit. Then it didn’t vent properly. I went back to using the one I was going to replace. Worth the extra money for an original I think. Dave

tbarb

The reproduction folks can't even make a gas cap, huh...

Whatever you do get that fuel up and vent your garage to get rid of the combustible fumes.

AkrHack

Sad but true I guess. If anyone has an unused original cap that they want to sell, let me know. In the mean time I've got my faulty repo cap on the tank, but only have it half way between off and fully tight.

MikeM

Hold your cap in "in car position" and see if you can blow air through the small hole in the center. Then flip it over and see if air will pass. It shouldn't pass air.

If it passes these tests, it is functioning as intended, at least while you were testing it.

Frankie the Fink

My LICS cap on the 63 is workingfine so far. You can dissassembe the old cap though to look for
trouble.

AkrHack

I will do the test, but I'm sure it is going to fail the "in car position test". The fact is that it already failed that test as evidenced by the excessive pressure that the cap allowed to build up in the gas tank. I consider myself lucky that I discovered the problem before the fumes could ignite.

Frankie the Fink

MikeM

Depending on the temperature, the tank can suck or blow. Sometimes, the valve in the cap will stick and it won't do one or the other.

AkrHack

I think in this particular case it had to be positive pressure in the tank rather than vacuum. If vacuum, it wouldn't have pushed gasoline up to and out of the carb.

vark_wso

Do you know if your replacement fuel tank has the integral pressure-vacuum valve? All GM SERVICE tanks for 63-E69 applications sold from the early 70's on for 63-E69 Corvettes DID INCLUDE an integral pressure vacuum valve. These tanks should be used with a non-vented cap, as in 70-74 Corvettes. Perhaps some aftermarket replacement tanks follow this design?

The valve, if present, is about the diameter of a quarter & is fitted about 5" toward the driver's side of the fuel filler neck, on top of the tank. On a convertible, the filler neck is short enough so carefully look left with something like a long dental mirror inserted.

See 'Note 1' on top, & cap specified in group 3.028 near bottom of page, below.

hedgehead

Run a 1/8 drill bit through the small hole in the center.

MikeM

That would destroy the internal check valve inside the cap. Maybe not a good idea if you get upside down.

65GGvert

I think you're going to eventually find that the gas cap isn't the problem. A whoosh is usually a vacuum and that wouldn't push gas toward the engine. Be sure to post what you find so we'll know the final outcome.

hedgehead

A dribble from the cap would be the least of your problems.

DansYellow66

Are you sure the tanks came prepped with a bung to mount this valve - but it wasn't included as part of the basic tank unit. I replaced mine in the late 80s with a GM service tank and it did not come with a valve. You can sort of see the plugged bung off to the driver side of the filler if you enlarge the photo a bit.

65tripleblack

See post #25 here:

https://www.corvetteforum.com/forums...working-2.html

Silverrick

Like Hedgehead, I re-drilled the hole. My "venting" issue was solved. Please don't tell the EPA!

MikeM

This is what I would recommend you do.

AkrHack

The prior owner that did the chassis restoration did provide one picture taken in 2012 of the newly installed gas tank. In the parts receipts he provided, I found the Zip Corvette purchases (which includes the part#) for the tank and cap. It looks like the tank in my car does NOT have the integral pressure-vacuum valve as some mentioned.