Fuel tank breather problem

BillyBob · Post by **BillyBob** » Fri Dec 29, 2006 12:42 pm

Firstly, a Happy New Year to everyone on the Forum, I hope to try and get to as many meetings/run outs next year weather and job permitting.
Unfortunately this year has just proved far too busy

I would like some advice on two questions I can't find any previous postings on:

1. If I fill the fuel tank up completely on my 1100S and and ride say 10 miles, there is a massive amount of pressure build up in the tank that I can only release by opening the filler cap. However, when I try and open the filler cap to fill the tank up from empty, there is such a vacuum that I have to claw at the filler cap with my nails to try and prise it open. Not easy on the cold mornings recently when your hands are freezing.
These problems only used to happen every now and again but over the last month seem to happen nearly all the time. I have checked the breather pipe on the filler top and it's clear. Should the seal on the bottom of the filler cap flex enough to release any pressure or is the problem elsewhere?

2. When I last bought a Vee belt the BMW Stealer said that as my bike was an early S (1999) I would need the Vee belt kit which included top and bottom pulleys, as these tend to wear more quickley than the later ones.
Nearly a year later I still have not gotten around to fitting the pulleys. Having just done a service on the bike, the belt appears in good nick with no fraying or cracking and has covered over 25k since it was fitted, so is it worth the hassle of replacing the top and bottom pulleys ?

Cheers for any advice.

nab 301 · Post by **nab 301** » Fri Dec 29, 2006 1:57 pm

I've a '99 model also ,bought with 14k miles currently 55k miles .I replaced the belt once. Wasn't aware of any pulley mods...
Nigel B

oyster · Post by **oyster** » Fri Dec 29, 2006 6:48 pm

On an early model, two hoses depart from the filler neck area via the inside of the tank and exit from the pump/filter assembly. These black hoses terminate behind the rear brake cylinder alongside the swing arm. Try blowinng through them from that end. One is the tank vent, the other is an overflow drain. Some fiddling about should let you determine which is which. Both should be unobstructed. Check they aren't kinked - common problem after lifting the tank.
I am suprised the bike will run to low fuel without a breather; shows how good the pump is!

r550s · Post by **r550s** » Fri Dec 29, 2006 7:05 pm

...maybe the tanks only 2.5" wide by that point.....
sorry

BillyBob · Post by **BillyBob** » Sat Dec 30, 2006 10:56 am

Cheers guys I will check both breather pipes later today.

Bloody typical, I filled the bike up this morning and there was no vacuum or pressure at all in the tank.

jivebiker · Post by **jivebiker** » Fri Jan 12, 2007 4:25 pm

Did you ever find out the cause BillyBob?

I have got the same thing happening now. The tank breather hose (connecting to outside the filler seal) is clear, but the other hose (overflow?) is blocked.

Ive just noticed this, but then I usually fill up leaving my house (about a mile away) but recently I have been filling up after a 10 mile blast. It could be a kinked hose since the last service.

Where is this likely to happen? do I need to take the tank off?

Any advice welcome.

oyster · Post by **oyster** » Fri Jan 12, 2007 6:47 pm

I suspect you have your hoses mixed! The pipe serving the outside of the filler seal is the overflow, the breather terminates INSIDE the tank. It's this one that if blocked creates the vacuum. The kink will most likely be on the 'frame' side of the right lobe of the tank, after it exits the solid pipe in the tank via the pump/filter plate. To check, work back up from the open end of the pipes near the rear brake and look for the kink. May require removing the sides, snorkel, then lifting the tank from the rear to check the full length.

jivebiker · Post by **jivebiker** » Sat Jan 13, 2007 2:29 am

Ah yes!. That makes more sense. The breather (inside the tank) is the one that is well blocked. Hooked the end of the hose to my footpump and got 50psi.

Looks like I'll be taking a peek tomorrow then.

I wonder how long its been like this, my last service was back in July!

hjr1100s · Post by **hjr1100s** » Sat Jan 13, 2007 7:12 pm

Aha! The tank breather problem. Had that one too. Replaced the breather unit that's bolted to the filling opening twice now: every 50.000 km's or so it's clogged up with some sort of alkaic limy boilerscale (?), thus preventing the tank to be vented.

No one could tell me why this happens. Maybe it's because I always fill her up to the edge while standing on the side stand. Don't know really.

Mine is an early '99 'er to. Never replaced the pulleys, never had extraordinary wear on the belt.

HJ

jivebiker · Post by **jivebiker** » Sun Jan 14, 2007 7:47 pm

OK,

I've had the bodywork off (for the first time), checked the hoses - all free and clear.

As HJ says the blockage is in that weird coily bit of pipe around the filler neck. Cheifly, the corrosion causing the blockage is at the points where the pipe is welded to the filler neck, mustve burned off the plating leaving exposed mild steel, fab.

I cleaned it out a bit with lockwire, and have now got adequate air flow, but this will not last. Does anyone know if a small hole in the bottom of the filler cap will allow breathing through its body?

This is the first time I've ever encountered this breathing arrangement. Has anyone rigged up any alternatives?

I wouldn't mind so much, but the process of sorting the problem, albeit temporarily, has bu99ered my back up, so I'm gonna be lucky if I can walk tomorrow! Fab!

Oh well another boxer lesson learned (and at least a few quid saved).

hjr1100s · Post by **hjr1100s** » Sun Jan 14, 2007 8:19 pm

To add to this subject: first time it occured, I've neglected the problem too long. The underpressure caused a failure on the bottom weld of the tank with massive gasoline leakage as a result.

My certified BMW dealer had it 'repaired' ..... with two components glue

thus making sure he'd lost another customer.

Had it welded properly by a non-BMW dealership.

HJ

julian · Post by **julian** » Sun Jan 14, 2007 11:50 pm

hjr1100s wrote:Aha! The tank breather problem. Had that one too. Replaced the breather unit that's bolted to the filling opening twice now: every 50.000 km's or so it's clogged up with some sort of alkaic limy boilerscale (?), thus preventing the tank to be vented.

No one could tell me why this happens. Maybe it's because I always fill her up to the edge while standing on the side stand. Don't know really.

Mine is an early '99 'er to. Never replaced the pulleys, never had extraordinary wear on the belt.

HJ

I had the same problem on my first '99 model. The metal pipe was clogged solid. I kept a spare key on me to release the tank pressure every 50 miles or so.

BillyBob · Post by **BillyBob** » Tue Jan 16, 2007 6:09 pm

Jivebiker,

Yep managed to fix the problem last weekend. I found the two brass coloured pipes on the filler cap assemley (breather and overflow) were both blocked with a load of crap. Tried blowing them out with an airline but in the end managed to almost clear them with a bit of wire and then left some Viacal descaler to soak in there for a few hours.

No more problems apart from the state of the kitchen sink, so the wife informs me....

oyster · Post by **oyster** » Tue Jan 16, 2007 6:29 pm

Something else to add to the list of periodic maintenance! I had not heard of this one before. I wonder what it is? Residual solder flux? Rubbish from cheap petrol?