gas cap doesn't vent

[Guest Brian Ash]

Sometimes, on my V11 (naked), the gas cap doesn't vent, so after a few minutes of riding, a vacuum is created in the tank. enough to make the tank suck in a little. when i open the cap, a rush of air flows into the tank, allowing it to expand again. i am surprised that the fuel pump is even able to get any gas out of the tank with such a vacuum. I assume that the holes under the cap are for venting... should i just disassemble the cap, or would that be a mistake?

[Guest russ]

Brian,

 

You have the dreaded Tank suck as did I on my LeMans.

 

Two things to do:

 

1. Remove the charcoal cannister and appropriate hoses. A previous post on this site.

 

2. Make sure your tank vent is working properly by blowing through with compressed air to dislodge any dirt. If this doesn't work a trip to the dealer for a replacement may be in order.

 

Hope it helps

[dlaing]

a couple other things to do:

3. remove or reposition the "tip over valve" If it is not mounted upright it will shut off the air intake.

4. remove the rubber nipple that you should see when you flip open the gas tank. I cut a little slit in my bike's nipple to let air pass.

WARNING removing of modifying either of these devices could cause fuel to spill all over you, the bike and the road in the event of an accident. Flames, death, pain, etc.

[Janusz]

The holes under cap ARE NOT FOR VENTING but for overflow draining. Your cap is good, get rid of pollution stuff and valve under tank.

[dlaing]

If I may revise my answer...

As Janusz said, "your cap is good"

The problem is the tip over valve. I came up with solution 4 (slit rubber nipple) before knowing about the tip over valve. If you want to fix it the 'perfect' way, find a replacement tip over valve from a bike which has a tip over valve that works. You may be able to simply re-position it and the problem will be gone! Some have claimed to do this.

 

Leave the emission equipment on the bike and save the environment! Or not, and give yourself extra room on the bike by removing the cannisters as the others suggested.

If you remove the cannisters, be sure to close off the lines to the intake manifold.

 

Removing the tip over valve will fix the problem but, is a little hazardous. Keep in mind that older bikes vented directly to air with no tip over safety features.

[al_roethlisberger]

Correct, all you have to do is orient the tip-over valve vertically(when it's not vertical, that's the problem) and lash it to the frame. I've attached mine to the front motor cradle/frame, and all is well.

 

al

[Guest odyssey986]

Does anyone have a picture of WHERE the tipover valve is and WHAT IT LOOKS LIKE?

[al_roethlisberger]

hrmmm, not likely.... as most are binned

 

 

It's easy. Look up under your tank, and there are two vent/drain lines attached to the underside on the midline, about midway to two small silver nipples. One is a vent, one is a drain. Follow those lines.

 

The drain will trail back toward the rear of the bike, where the vent line(which has the tip-over valve) goes either straight down, or back a bit as well, but generally is on the right side of the bike/tank.

 

Anyway, the tip over valve is a small black cylinder, about 1.5 inches long, attached in-line with this vent line. It has nipples/barbs on each end that the line coming from the tank, and coming out of the valve to drain to the ground. You really can't miss it.

 

If you look up under the nose of the tank above the right cylinder, you'll probably just see it dangling about under there. If not, if you lift the tank up, you will certainly find it post haste.

 

Once found... rip it off , and replace said two pieces of hose with one length, or just junction the two pieces together with a bit of vacuum hose nipple to make a continuous hose.

 

Hope that helps.

 

al

[al_roethlisberger]

The holes under cap ARE NOT FOR VENTING but for overflow draining. Your cap is good, get rid of pollution stuff and valve under tank.

 

 

....aaaaaactually, the left hole is for drainage, and the right hole(with the raised turret) is the vent. However, if during an accident the bike is on it's side, it will TRY to drain through the vent

 

That turret mates with a rubber grommet(black or red) under the cap. This preserves the air/fuel-tight seal when the cap is closed, but allows vapor to vent through the neck, up through the cap assembly, then back down through the rubber grommet, then "turret", and back down through the tank inside the encapsulated vent line, out the bottom nipple... and normally, away through the tip-over valve and vent line.

 

 

...however, if the tip-over valve is blocked/malfunctioning, this venting/breathing cannot occur, as there is no other outlet for the tank. And then we get the dreaded "tank suck"

 

 

The left hole however is an overflow/drain, but is outside the sealed neck of the cap, so only drains overflow/water that has somehow sloshed into the area around the cap.

 

I have a bunch of photos of these vents, drains, and the differences in the 2000-2002, and 2003+ tanks in my 2003 tank retrofit thread if interested.

 

al