Fuel Cap Venting?

Johnthemann · Posted: Sun Sep 21, 2014 4:43 pm Post subject: Fuel Cap Venting?

I was driving my 74 around earlier today and all of the sudden it acted like it was running out of gas. I had just filled up so I knew it wasn't empty. I pulled the fuel line and realized I wasn't getting any gas to the carb...fiddled around with the filter and it looked good so I pulled the line going in to the fuel pump and immediately heard a hissing sound like pressure being released. I had an ahh moment and opened the gas cap to even more pressure being released. I reassembled everything and as expected the car started right up and ran perfectly for several miles until it again pressure locked. Is the cap on the Thing vente or is there something else I should be looking at. I did a quick search and couldnt find much.

mondshine · Posted: Sun Sep 21, 2014 5:28 pm Post subject:

The fuel cap itself is not vented.
Maybe this drawing will help you locate the problem.

Image may have been reduced in size. Click image to view fullscreen.

Good luck, Mondshine

Al Capulco · Posted: Sun Sep 21, 2014 10:45 pm Post subject:

I believe they are vented. That is why they have the spring loaded diaphragm. If you don't have the right cap or the cap is defective you could have this problem.

Kiptere · Posted: Mon Sep 22, 2014 2:33 am Post subject:

I just took the gasket off my gas cap. Problem solved. No gas leaks out.
_________________
62 Bug
70 Bug
68 Bug
70 Bug Vert

Johnthemann · Posted: Mon Sep 22, 2014 5:02 am Post subject:

Thanks all for the tips. Im going to start by removing the gasket and see where that gets me Very Happy

74 Thing · Samba Member Joined: September 02, 2004 Posts: 7391

The gas cap is not vented and do not remove the gasket-that will just lead to gas vapors and spills on your fender when you drive as well as your garage being filled with fumes which is dangerous.

There is a vent on the tank on the drivers side. The vent must be clear or it will create suction on the tank and gas will not flow. If you remove your gas cap and hear a swoosh sound then the vent is clogged and you need to fix it. The vent line runs from the tank up to the top of the luggage compartment where it tees into another fitting the down the drivers side and into the expansion chamber. There is another house to the expansion chamber that runs underneath the tank and is attached to a metal hose near the brake master cylinder. This metal hose rusts over the years and is usually the source of the problem. You can remove the metal hose all together and replace it with hose or usually if you cut off 1-2" at the end it gets rid of the rusted part. Blow through the hoses with an air compressor or use your lungs. If everything flows again you should be good. That hose eventually runs down the passenger side of the car and up under the rear passenger side wheel where it connects to the charcoal canister which should be attached to the oil/air cleaner so the fumes can be burned.

Look at an early bug vent set up-they run a hose up high in the luggage compartment then back down and the hose runs underneath the gas tank near the horn area and vents to the ground-this is an alternative for you, but regardless you need a vent. I have heard of some instances where the suction is so great that the gas tank starts to collapse.

IHC · Posted: Mon Sep 22, 2014 7:52 am Post subject:

74 Things idea works best.Early bug style vent.Have used that method for years and never had venting problems again.do not remove the gas cap gasket.Hot days and parking unlevel will dump your gas down the side of your car.

Johnthemann · Posted: Mon Sep 22, 2014 10:34 am Post subject:

Good information. I wil go this route. Thanks a bunch!

Al Capulco · Posted: Mon Sep 22, 2014 8:25 pm Post subject:

I have the same gas cap that Mondshine has and that cap is vented. The center part is spring loaded to allow pressure to excape. I understand how the gas tank fuel vapor is vented, but if you used this type of cap it too is vented. Type 2 buses use the same cap. There are different caps available that will fit that are not vented, but they don't work very well if your fuel vapor lines are not clear.

mondshine · Posted: Tue Sep 23, 2014 8:04 pm Post subject:

I think the stock gas cap will let pressure escape if pressure in the tank can overcome the spring tension (like a radiator cap), but I don't think it will let air into the tank when a vacuum is formed with fuel consumption.
This is the problem described in the original post.

I had this problem with my '71 Super Beetle, and the vacuum actually (partially) collapsed the tank! I had to do a roto-rooter job with heavy piano wire to clear one of the steel vent tubes.

Johnthemann- I hope you get it sorted.
Good luck, Mondshine

Johnthemann · Posted: Thu Sep 25, 2014 6:56 am Post subject:

[quote]I had this problem with my '71 Super Beetle, and the vacuum actually (partially) collapsed the tank!

I crushed the tank on a BMW 1150gs like a keystone light can because of a clogged vent. Cool


Hello! Log in or Register \| Help \| Donate \| Buy Shirts	See all banner ads \| Advertise on TheSamba.com

	Forum Index -> Thing/Type 181	All times are Mountain Standard Time/Pacific Daylight Savings Time
Page 1 of 1