Fuel running out from vent hose -91 851 Strada

Desmo851

Hi!
Searched the forum, but could not find this topic covered.
I have a newly serviced 851 that is running fine. Just bought it and it had just enough fuel to start it and drive it round the block. No problem. Filled it up with fuel, and the vent line spills it all out on the ground perfectly. I temporarily closed the line, bought a plastic gasoline tank and flushed what was left in the tank into it. I have seen the wiring diagrams for the different hoses and pictures from inside the tank in this forum, so i have a fairly good overview of that.

- What is wrong when the fuel is spilling out like this?

And how is the external configuration of the different hoses on the tank? Have not removed the tank yet, but i can see underneath that the vent line is connected two different places on the tank and via a plastic Y-connector is merged into one that runs towards the ground. Anyone has pictures of the underside of the tank, with any specification?

Any help appreciated, thanks a lot.

Foggy 888

There are two metal pipes that run from the top of the fuel tank through the tank to the bottom of the tank and out the vent hoses. One pipe is a drain that allows overfilled fuel and rain/water when you wash the bike to drain from the area around the filler neck. The other is connected to the vent system that is built into the gas cap. There is a rubber seal that fits in this port and seals against the gas cap when you close it.

The only way that fuel should come out of either of these pipes is if you either overfill the tank and the excess comes out the breather, or if you spill fuel into the area next to the filler neck. In either case only a small amount of fuel will come out and then stop. If you have filled the tank and fuel is just running out of the vent pipe, then one of the metal pipes is damaged inside the fuel tank and the tank will need to be repaired or replaced.

Desmo851

Thanks for the insights, Foggy.
I dis-assembled the fuel filler cap completely yesterday (quite a struggle - wow!), and got to see what was going on. Luckily nothing serious and not in the market for a new tank.
The vent line that exits the tank, and usually connects to the filler cap, had fallen off the filler cap connector and was head down in the bottom.
Physics explain why so much gas was drained after i filled up the tank, so that makes sense. Nothing broken inside, but i will replace most of the lines inside the tank because they looked rather beaten up with split ends etc. Just make sure i buy items that allows for soaking in fuel.

It`s probably not unusual, and i know this by experience as well - when you start to dismantle stuff for replacement, you ALWAYS find other stuff that could need attention as well. On this one, i limit myself to only change internal and external lines to and from the tank + redo the heat shield as the original one was missing and the previous owner did a shitty job with some self adhesive stuff...

Foggy 888

I forgot that there were rubber hoses that connect the filler cap assembly to the metal pipes. Glad that it was something that was fairly easy and inexpensive. Replace the fuel supply hose from the pump and the filter in there while you are at it. You only want to do this job once every ten years or so.

Desmo851

Yup, nothing major and that was great.
I actually tried to get a hold of all the in-tank lines for several days, but ended up just re-doing some split ends in there. I could not find what was needed, due to no one having fuel submersible lines available - nor could they tell me where i will find this.

If you have any information of who can deliver these, please advice. I will probably change them all including filter after the season.

First trip on the Old Lady yesterday :-)
Thank you very much for all input.

Mr.R

I get my submersible hose from a BMW dealership, they sell it by the metre and it doesn't cost that much.

Steve R

marvin

Ebay

Desmo851

Great, thanks. I will try some local BMW dealers first.

stafford

With regard to the picture above of the underside of the 851 tank showing the four connections, obviously one is feed another return and two are drains. If one drain goes to the underside of the fuel cap where does the other connect to?
I have run out of things to plumb the 2nd one too.

mikesps

The second hose is for the tank breather under the cap. That style has two hoses connected to the insert that the cap attaches to.

stafford

Ah, I have a later cap that only has one drain as the cap is the breather.