Gasoline defying gravity

[j98sprint]

Gas bubbles up through the keyhole in the gas cap after a ride when the tank is full.

Is there a one way flap in there that needs replacing?

[crazymadbastard]

check all the rubber hoses leading out of the tank, there should be no kinks.

report after that.

[Kevin1956]

If it's not kinked vent hoses, you're filling it too high maybe? Heat expansion may be causing this. The gas comes out of the underground tank fairly cold and will expand a little in the heat. You're in nice warm Florida, right? On a California model gas can get in the smog crap, and it will quit running because the fuel blocks the vents not allowing air in. It can even happen if you drop the bike and it lays on it's side too long. I never fill mine even high enough to touch the metal cup below the gas cap opening, always leaving a little gap. So what if it's not 100% full? By the time you burn a tank of gas you're ready to get off, refuel, and stretch your legs anyway. On the older 250s, put your gas in while the bike is on the kickstand, not the centerstand. This will help from over filling too.

BTW: My '12 model has a sticker on the tank warning about this. It makes me wonder, is this the reason why new gen models didn't come with a centerstand?

[j98sprint]

No kinks and not over filling. Been riding this bike in hot-ass Florida for 8 years. Just started happening.

Thought maybe someone had experienced something similar. Guess I'll take the cap apart and have a look.

[Ghostt]

There is 2 diaphragm valves inside the gas cap itself. As they get older, they loss their flexibly.

Personally remove and disassemble the cap, and remove them, they are often the cause of vapor lock, poor fuel flow, etc.....

Here's some pictures to help you out.

[j98sprint]

Thanks for the helpful reply Ghostt. I took it all apart before I read your post and found those red rubber discs. The location in the cap had a lot of whitish flakey stuff. I just cleaned everything and reassembled.

Are those red rubber discs supposed to keep rain water out or gas from splashing up through the cap? No problem either way with those discs removed?

Let you know if the cleaning works. If not I'll try removing them.

[Ghostt]

The intended propose of the diaphragms is in the case of an accident it prevents fuel from spilling out.

No worries, just remove them, as they cause more problems than they solve, if you do happen to lay it down, the worst is a few drops of gas, at best.

These diaphragms are the leading cause of tank vent issues.

I myself have done it to both of my bikes.

The cause of water in gas tank is the tank drain, which is that line coming off the back of tank. I would advise that you blow that line out via an air compressor, as I've had an issue with it being clogged on the EX500 which was the cause of water in my tank.

[j98sprint]

Rode this morning. Full tank, no violations of the law of gravity (no gas bubbling up through the keyhole). The clean-up worked.

I'll yank the red rubber discs if the problem return.

[FrugalNinja250]

There is a seal in the bottom of the lock cylinder hole where the connection is made to the latch mechanism. That seal has nothing to do with the venting system that includes the red valves. You need to replace that seal. Until then, you can fill your tank to a level that's a bit lower than you've been doing, that will keep the fuel from getting to the latch mechanism when it expands from heat.