Another gas cap question

Ross/Kzoo

Ross/Kzoo

Well-known member
The last couple of weeks I took my speedster to the Wed cruise in @ Gilmores. Both times after about 5 minutes of running I'm going about 40-45 and the motor cuts out and slows down to just above an idle and then picks back up and proceeds to do the same thing again. I limped home, not too far and checked it out this morning. I cleaned out the fuel bowl and there was a small amount of debris but that didn't seem to be the problem I then looked at the gas cap to see if there was any restriction. To my surprise the rubber gasket was swelled like sponge and it felt like one too. That may be my problem so I'm considering making a new gasket out of the paper/cardboard type gasket material. It appears that the only purpose is for sloshing gas coming out of the cap. Does this sound reasonable or is there a better fix?
 
The gasket is just to keep gas from sloshing out, there should be a small hole in the center of the cap to let air in. A deformed gasket may come apart and drop pieces into the tank.
 
The fix sounds OK. The problem is ethanol, it swells rubber. If you can still find real gas, use it before the ethanol causes more problems.
 
Sounds to me that the vent it the gas cap is plugged off. A Model A must have a vent to the tank otherwise a vacuum will occur and prevent the gravity flow of fuel.

The 30-31 reproduction gas caps (and there are thousands of them in service) have a quality flaw. There is a large rivet in the center of the cap that goes from the bottom up through three elements. The metal tank grabber, the gasket, and a brass washer. A small hole is drilled through the three elements to a void in the roof of the cap. This is how the cap provides a vent.

Over periodic use, the twisting motion of taking the cap on and off will cause the rivet to becomes loose and allow the there elements to rotate out of position and plug the vent off.

There is a repair. If the three elements are out of position drill another vent hole. Be careful not to go through the roof of the cap. Drill a second hole opposite the vent hole and tap it for a 6-32 thread. Install a screw and lock tight it in place. This will prevent the elements from rotating.

The cap in the photo was repaired in a similar manner. After I drilled the second hole I installed a rivet and used JB weld to hold it in place.

Snyder's sell an Eaton cap that is identical to the original, it has two rivets with a double vent hole, and is of good quality.

Tom Endy
 

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  • 30-31 gas cap vent.JPG
    30-31 gas cap vent.JPG
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RG&JS Area 15 page 15-8 revised 1997, Check for a leather gasket in the gas cap.

for the 30-31 Bratton's part number 12970, $1.10
 
I have shown pictures of the 28-9 gas and radiator caps taken apart, so it's easy to follow the vent path. Maybe a search will find the pictures.
 
Sounds like a similar problem I was experiencing. I found the gas valve under the dash was clogged. To verify, I cleared it by slowly purging the valve with air hose. Gas flowed normally after to clog was cleared.

Now, to clean gas tank...
 
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