vented gas cap leks fuel?

are you missing the filter like this?

All I can suggest is using your idea to run a tube off of the cap itself or installing an auxiliary vent in the fuel tank. An internal tube running from the top of the tank near the filler hole and out the bottom floor of the tank. Like a stand pipe would be installed.
This is how modern *sold in California, street legal* motorcycle tanks are vented. It is the only way the Mfg's can vent the tank through a vapor canister to comply with the CARB reg's. The "vented" caps sold in California only vent air in, nothing out, so as to not cause a vacuum in the tank as the fuel level drops.

Yeah, it sounds like alot of extra work, but if you wanna keep the look of the cap clean without a hose on it...

I have a suspicion that you are developing pressure inside the tank as the gas sloshes and vibrates inside, causing it to vaporize some. The pressure has nowhere else to go but through the gas soaked screen in the cap forcing the gas out of the screen and out the vent hole. The stand pipe vent would solve this problem.

Here is the mod like GearNut mentioned. Works nice.


Sportsman 200 by Sportsman Flyer, on Flickr

I have the same setup as Pat, I also install the breather tube with a check valve in it. I purchase them from the local motorcycle shop.

The vent in the bung king work poorly, we have all dealt
with its issues.

So the tubes work better than constructing some kind of anti slosh baffle? Or do you two, Sports and culver incorporate both into the design set up?

Goat Herder said:

So the tubes work better than constructing some kind of anti slosh baffle? Or do you two, Sports and culver incorporate both into the design set up?

Click to expand...

A large anti-slosh baffle may work just fine, but I have not tried them yet. The small internal check valves, ones inside the breather of the cap, help but do not correct the problem completely. The external barb fitting and hose is really simple and works. I also find different engines have different vibration zones that lead to problems. The big four strokes, at least for me, seem to have venting issues low in the rpm range while high winding two strokes leak more at high speed cruise. I find the hose fix works well in both situations.