Gas cap leak

Ed Saniewski

Ed Saniewski

Well-known member
I have a problem with the gas cap on my 29 CCPU. When I fill the tank up close to full, but still a few inches away from the top, after a while I notice gas leaking out on to the top of the tank. I am sure the gasket is tight because it looks like it is rubbing on the top of the neck. Is it coming out the vent hole from splashing? I run a spark screen because I thought that would keep the splashing down. It is a re pop cap. Has anyone come up with this problem, or better, a fix for this? Thanks, Ed Saniewski
 
Do you have an original cap? I always fill to the top and don't have a problem as long as I use an original cap. Some repro caps have a hole through the center, and I can see where this would leak with gas near the top of the tank. It could also allow water to get in during a rain.
 
Tom Wesenberg said:
Do you have an original cap? I always fill to the top and don't have a problem as long as I use an original cap. Some repro caps have a hole through the center, and I can see where this would leak with gas near the top of the tank. It could also allow water to get in during a rain.
Click to expand...

Don't all 28 29 gas caps have a small hole? The radiator cap is solid.
 
jmeckel said:
Don't all 28 29 gas caps have a small hole? The radiator cap is solid.
Click to expand...

The original gas caps had 6 very small holes around the outer threaded part, and this led to passages between the inner and outer parts of the cap. I posted pictures of original caps taken apart (unsoldered) and a search for "original gas cap" might turn it up.:confused:
 
I didn't have any luck using the search feature, so here is a picture I had on my computer of the radiator and gas caps. The cap on the left is a quality steel repro gas cap. The middle is an original brass gas cap and the inner brass part is shown on top. Notice the 6 thin slits for venting.

The right side shows two styles of original brass radiator caps, with NO vents.

Of course both the radiator and gas caps are nickel plated. I took mine apart to repair some dents and haven't replated them yet.
 

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I have the same issue. I have a cap that looks like the one Tom calls the quality steel repro cap. (From Berts) except mine has a cork gasket. My old cap had worn threads and would not tighten, I was always afraid that the tank threads were worn some as well, so I never tightened it very snug. After reading this thread, I went ahead and tried snugging it down and it was fine. Whether or not it will still leak remains to be seen. I don't have a spark arrestor in mine.
 
Tom Wesenberg said:
I didn't have any luck using the search feature, so here is a picture I had on my computer of the radiator and gas caps. The cap on the left is a quality steel repro gas cap. The middle is an original brass gas cap and the inner brass part is shown on top. Notice the 6 thin slits for venting.

The right side shows two styles of original brass radiator caps, with NO vents.

Of course both the radiator and gas caps are nickel plated. I took mine apart to repair some dents and haven't replated them yet.
Click to expand...

Thanks Tom, learned something new!
 
I cut a new leather washer, and drilled 3 small holes. The hole inside the top of the cap is quite large and this should do it. Thanks for the help, Ed Saniewski
 
Is that a "Piet" by your pickup? I helped my buddy on his Corvair powered one.

In any event, is the fuel tank venting only thru the cap? My 601 had a seperate vent and I don't see any holes in the cap on my newly acquired 1930A project.
I have no indication of a fuel lack.

Dick
Lakeland Florida
 
Re: Gas cap vent

Tom, I regasketed, replaced float on the fuel gauge and new screen to glass filter bowl.

Now it appears engine starves when cap on tightly...

My question is where does fuel system get vented to avoid starvation? I
See no vents/holes in my cap.

Thanks, Dick
 
You need to get yourself an Original gas cap, they are vented around the bottom of the cap.if you look at tom picture the ones on the left is gas caps,
 
I think I've miscommunicated: my A has a '30 cap and per 'mACs' is vented. I just can't see the vents and apparently it has become non venting while fixing some leaks ...

Surprised that a little weeping at the gage and glass filter bowl would allow trial running of engine if the cap was non-venting all along. Just used to aircraft system venting.

Anyway, thanks. dick
 
I think I've miscommunicated: my A has a '30 cap and per 'mACs' is vented. I just can't see the vents and apparently it has become non venting while fixing some leaks ...

Surprised that a little weeping at the gage and glass filter bowl would allow trial running of engine if the cap was non-venting all along. Just used to aircraft system venting.

Anyway, thanks. dick
 
Yes it is Dick, there were two of them at the national meet in Oshkosh WI. I got the chance to drive out onto the field for the picture after meeting the owner of the plane.
 
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