Gas tank leaking

[AtLarge]

I went out for a spirited ride on Saturday.  All was well and the bike actually ran pretty well.  I intentionally put as many miles as I could to run the old gas & seafoam mixture out of it.  When I felt I had pushed my luck far enough I stopped and filled up the tank then went home with a smile on my face.  Go out to the garage today and find this and the fumes were thick.

Well, crap got a leak.  Drained about 3.5 gallons of gas out (most I could get), pulled the seat and knee pads then went in and started doing my research before I go any further.  Since I have no pressure in the tank I can disconnect the gas lines with a minimal amount of spillage and spray but, after looking around I have to wonder if I really do have a leak?  Is it possible I just overfilled the tank?  I topped it off about two inches from the small filler door.  It's all on the right side and when I look at the fiche I see a vent hose but, the picture doesn't show what it connects to.  Is it on the right hand side and does it run down to the foot peg and then towards the rear wheel from there?  I see a hose that does that (it's cracked) and it goes up towards the tank but, I can't see much from there without lifting the tank up.  Could be the vent hose it broken farther up too which is why it's raining down on the air cleaner box?

[Bon Jon Bovi]

In this pic you can see the larger/ forward vent hose going down to a gray canister valve, then down to the top of the crankcase. The smaller/ rear vent hose is hard to make out to the left of the larger hose, is smaller and worms its way to the rear as you say.

[volador]

In the above picture of Bon Bovi you may remove/omit the tubing and gray check valve and cap off the tubing nipple/stub on the front of the block under the radiator shroud.
Or leave rubber tubing and gray check valve in place and disconnect from tank vent and plug rubber tubing end with a bolt or suitable hardware.
This was BMW evapoative emission compliance of the time but later removed.

Service Bulletin 2228

[volador]

During moto use its possible for petrol and fumes to be expelled from tank especially when full. Sloshing petrol can be sucked up into the tubing vent and expelled under tank pressure.
Exterior petrol tank bottom has 2 tubing nipple piped into the tank for petrol fume vent and the water/rain drain collected from around petrol tank cap.

The hole at 6:30 is the petrol cap water drain. The notch in the petrol tank cap base has to line up to that hole. The indicated tubing end is the internal tank vent.



1985 K100 petrol tank bottom for illustration purpose of tubing nipples. Disregard upper tank left, K75, K100, K1100 have different outlet and return tube nipples for petrol.
Forward nipple is tank vent, rear nipple is water/rain drain



K75, K100, K1100 may or may not have the air accumulator cup 16132307467 installed to collect any expelled petrol or water from tank nipples with 1 rubber hose connected and routed down to back of right footpeg plate.
Or instead 2 rubber hoses will be connected direct to the petrol tank tubing nipples if no air accumulator cup. Again hoses routed down to back right footpeg plate.

AIR ACCUMULATOR CUP




AIR ACCUMULATOR LOCATION

[AtLarge]

Thank you Gentlemen!  That helped immensely.  I pulled the tank off.  No clips on the posts so, the bike is Chris Harris compliant.    Also found the cup was still installed but, no hose for it and the check valve delete had already been performed on the nipple of the crankcase. Both the twin tubes at the top of the tank are bare and that's right over the air box so, I think that is indeed what peed on it.  With that I am happy there are no hole pin holes in the tank. It's too cold and too late to do anything else for tonight and left the tank flipped on it's side with a fan blowing on it to try and evaporate the gas soaked insulation.  With a clearer mind and understanding I will go back and look for the rest and go from there.   

[AtLarge]

Well, it just got worse.  Now that I have things dried out and can follow the tracks it actually is leaking either around the fuel gauge flange or one of the screws holding that in.  Looks more like just one screw in particular.  I tried just running a screw driver over all four and their tight.  None would budge.  Does anyone know if there is a suitable substitute for that o-ring 62161459608 that I could pick up locally like at an auto parts store?  My nearest BMW dealer is 30 miles away and none in stock of course.  They or I can order one but, would like to try to beat that if possible.

[AtLarge]

Oops.  Double tap.

[The Mighty Gryphon]

Is this the o-ring that seals the mount for the Fuel level sending unit? 

If so, take the plate out, remove the o-ring and take it to almost any place that sells bearings and shaft seals.  They can measure the old one and give you a new one.  Should cost about $7, if I recall properly, for viton.

[AtLarge]

Cool.  Thanks Gryph.  Will try to do that Monday.   

[AtLarge]

Well that Monday came and went.  Mostly because of the whole quarantini thing and I just didn't want to deal with it going about town.  Instead I ordered it from Max along with a couple small cosmetic parts.  The original had to be OE because it was pretty hard.  Installed last night and added gas.  Was still holding this morning so, I commenced to motobrickin this afternoon.  All is well and I even replace that drain hose from the cup with some stock I had on hand.  Now I'm off to things of lesser importance like leaky fork seals and disc's that sound like a herd of clydesdales.