Greetings fellow Dubyaheads,
Long time lurker, first time poster here. I have a 2000 W in great running shape despite having sat outside and unridden for at least three years prior to my acquiring it in 2016, but over the last 6 years I have been unable to solve a problem that is particularly troublesome. If the tank is more than half full (or half empty depending on how you look at it) It will leak gas out of the filler cap when warm. As it seemed like what would happen if the vent tube was clogged I replaced the hose on the vent nipple but did not improve the situation. I also replaced the filler cap to no avail. I ran it like this for four years simply never filling the tank more than halfway as a non-solution solution. I took a break from riding it over the past two years and when I got it back on the road last week I was determined to solve the problem this time by focusing on the metal vent tube that goes through the tank. I used a guitar string to ream it out and got it to a point where it seemed like I could feel air out of the hose when I shot compressed air into the vent hole under the cap. This seemed to solve the problem, but I noticed a very small amount of fuel at the end of the hose after a short ride, indicating that the vent tube in the tank was compromised by my reaming with a steel guitar string. Even worse, the tank cap leak came back shortly thereafter.

So my question is whether the tank vent system is the only possible cause of my filler cap leak? One thing that might be important to know is that the fuel cap was stuck shut when I purchased the bike. Secondarily, as it now seems that I have created a pinhole in my vent tube, and have not had luck with finding local bike or auto body shops that want to work on fixing the tank, is there anyone on this listserv that knows of a repair shop in northern california that will or has a spare fuel tank in usable shape that they want to sell?

Thanks in advance for any help or advice.

After some time to ponder my predicament I am now thinking that the small amount of gas that got into the vent tube was from the weeping gas around the filler hole, which is back in full force. Thinking this had gone away I had jumped to the conclusion that any gas in that hose would have to come from a leak I caused reaming out the metal portion of the drain tube. So I am no longer as convinced I need a new tank (unless there is a pristine stocker in an interesting color in someone's shed) but am at a loss for what to do next to fix the persistent weep of gas from under the cap when I park it on the side stand mostly full and even on the center stand when the tank is full, seemingly motivated by running the bike or hot days. If there are any gas tank vent system experts out there who can take me to school, or anyone who has seen a simialr issue and can throw me a line on what is causing it, I would be all ears and thank yous.

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You may have all ready answered this; however, I’m just jumping in with limited experience with similar problems on a 1970 CB350 tank and various sixties Honda ninety tanks. Have you replaced the original fuel cap gasket yet. For me, doing that one thing, and cleaning the cap thoroughly has fixed leaks around the cap. That’s five for five, but sixties Hondas had cork gaskets in their gas caps. I believe Honda had a rubber one that superseded the cork for the ‘70 CB350. Forgot one—1974 DT250A. Six out of six.

--
John H. in Omaha
2000 W650
2006 Vino 125
1981 CT110 “The Goin’ Postie Bike!”

Thanks John,

I take it from your post that in your experience this issue is not due to poor venting but a poor cap seal? I had already replaced the gas cap, which came with a new main cap gasket, but your post inspired me to take the cap off and look around. When I removed the cap assy, I found two old and stiff o-rings between the cap mount and the tank where the mounting screws enter the tank, ordered new ones and am hopeful that replacing them could solve my problem.

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I’m hoping for you that this is the ticket!

--
John H. in Omaha
2000 W650
2006 Vino 125
1981 CT110 “The Goin’ Postie Bike!”

Update:

it turns out it wasn’t the old O rings that were there, but an O ring that was missing between the tank tube at 4:00 on the filler neck and the tapered nozzle thingy on the cap (part 92030-1030) that was causing my issue. Missing since I bought the bike in 2016!?

This part was available and arrived in a week. $6 and two minutes later my problem was solved.?