Fuel dripping when engine warm - cause?

[voodooskin]

Yesterday smelled fuel while riding. Stopped and a healthy dripping from the overflow hose behind the right peg plate.  Tank was not full - closer to reserve than anything.

I have the "cup" air accumulator installed so fuel would have to be making it into the cup to flow out the hose.  Through some watching during my ride the drip only appears to happen when the bike is hot (fan just ran) and is repeatable.  Fuel qty in gas tank does not seem to matter.

I'm on the road and not in a good place to pull the tank and look, and have a multi-day ride home.  Curious what you think could be going on here?  When dripping its a healthy drip not quite a stream but almost.

Thanks!

[Elipten]

Is vent hole on gas cap closed?

[Sebsi]

This may or may not be your problem and solution:

http://www.motobrick.com/index.php?topic=4658.msg29190#msg29190

I had the exact same symptoms and fixed it as described. What was happening, I think, was that when the fuel return line from the FI squirts back into the tank (you can watch this: open the gas tank without the key on, then turn it on and watch/hear/feel the fuel squirt into the tank in the far upper right from driver's position) the nipple is positioned (mis-positioned, actually) so that when the tank is hot, the fuel/vapor is somehow squirted almost directly into the overflow line, which runs down to your air accumulator and out the line by your right peg. If this is what's happening, see the thread above for the fix. It's a tough one but do-able.

My guess is that there's a couple millimeters of wiggle room for the return spray and some German lumpenprole had a bit too much pilsner the night before.

Good luck,

Blake

[voodooskin]

Thanks Blake I'll take a look.  The fix for you was "extending" the fuel return with a hunk of fuel line/hose clamp?  Thx!

[Sebsi]

Yep. It's now a year later with no problems. Try to find a submersible gas hose that's bigger than the factory gas line and it'll make things a helluva lot easier. I forget what the size of the line in the tank connected to the filter, so find out what that is and move up a notch. The nipple is NOT the same size as, e.g., the nipples on the pump, filter, etc.

Blake

[rbm]

The BMW part number for that hose is 16131455350.  It is longer than required (1000mm) and needs to be cut.  It gives you at least two pieces.  One end connects to the return spout just by the gas cap and the other end fixes to the fuel pump filter screen.

[Scott_]

There is a BMW tsb that describes this procedure. It was intended for alleviating fuel pump noise, but it applies here as well.

[Sebsi]

Good luck with pulling off what's depicted in Fig. 2. Metal that isn't supposed to bend doesn't bend too well. I busted a screwdriver trying to do exactly what's pictured and cut up my hand pretty good. Ahhh, blood and fuel, a rich mix!

I wonder why this TSB doesn't address the heat/overflow issue, which occurs regardless of whether the tank's low or not. And the fix certainly doesn't do anything with fuel pump whine at low levels...then again, I didn't see the TBS when I did mine, and did not route it back towards the pump because by then I was bruised and bloodied and my clothes had finished drying at the laundromat outside of which I doing this procedure and I didn't give a shit anymore.

Blake

[voodooskin]

Thanks you guys for the info on this.  It looks like I can ride with this till I'm home and will fix it there.

Peace of mind knowing the situation.

[voodooskin]

Just a followup:

Before leaving Colorado to ride home to Oregon, got sick of the constant dumping of fuel so lifted the tank and stuck one of those rubber vacuum stem plugs onto the fuel tank overflow tube.  I had exactly one of those vacuum plugs in my spares kit.  Snug fit.

Did stop the leak of fuel, but also seemed to prevent the tank from equalizing pressure.   At one point in Utah, after getting stuck in a road construction delay on a 90-something degree day with the bike HOT now, went to open the tank fill hole at a gas station and the tank was so pressurized it just erupted in fuel and vapor out the fill hole - over the tank, instrument panel, tank bag, etc.  -  really impressive, fuel everywhere, lots of hot fuel vapor goodness.  Everywhere.  Very good there were no open flames nearby.

Other than that one time, no issues.  On returning home added the BMW official fix, the hose from the return down to the fuel pump area (and pulled off the vacuum plug), so far no leaks or issues.  I did have to bend the return tube to accept a hose, but had a 'tool' in my toolbox which I inherited from an old boss: a craftsman auger or screwdriver ground down to a gradual point, bent at a 90-degree midway.  It fit perfectly into the tube that needed bending and provided sufficient leverage and support to make the minor adjustments needed.

Thanks again y'all for the peace of mind and solution help, awesome forum.