After a short ride and a thoroughly warmed engine I pulled my K1100LT into the garage.  In the quiet garage and with the engine off, I heard an unusual noise. Upon investigation, I found it was related to the fuel tank.  The fuel tank interior had a vacuum or, was pressurized, verified by a "whoose" as I opened the cap.  
Is this normal?

Not normal. I would say my prayers. Thank gawd there was no BADA BOOM

Definitely not normal the tank is vented through one of the small tubes at the right rear under the tank.
I have wasps that like to build nests in everything like that and I need to put covers on all the air inlets to my spray guns.
The pump and fuel supply usually isn't compromised by a slight vacuum or pressure. Use a bit of edge trimmer line to clear the hole (here in Oz we call them wipper snippers and the poms call them strimmers but I don't know what you call them).
The rotten buggers even built nests in the outlets to the drains for the sunroof of my X5 and it caused a massive flood inside the car and filled the glove box with water.

I call the landscaper he deal with wipper snappers or strimmers or whatever your talking about

had my gardener spray down the X6 with DEET rid those bloody daubers

Humm.  It sure didn't seem normal.   I'll confirm that this is the season for those dreaded wasps and they sure are active around the house and garage now.  However, I have never before heard that they clog vents.  I've had the fuel tank off fairly recently and I reconnected both the tubes a bit right of the center line of the tank's underside when I replaced it. I took those to be a water drain and a vent to atmosphere. The water drain runs toward the rear of the bike, but I don't know where the other ends up.  "The other" being the larger of the two tubes, I suppose an insect could find it attractive.  I'll have a closer look tomorrow if SWMBO doesn't have other plans. 
Thanks.

On my vintage the two drains sit in a frame mounted cup with a single outlet pipe routed near the rear m/c. Either way I imagine the function is the same. One is to take water away from the channel under the tank cap, the other is to take excess (heat expanded) fuel off the top of the tank. 
Just in case, you haven’t by any chance reinstalled the tank cap backwards, as that will block the top breather hole too?

Aircraft > Pitot tubes >wasps, hornets > Crashes. Same thing.

Time to overhaul the tank cap
(Been there, done that )

I had a look at the bike this morning.  I learned nothing I didn't know before, except that she fired right up at the touch of the button at that time.  I removed the cap.  It had been installed correctly, so no issue there. Is it time to rebuild the cap?  How does one determine that?  There is no obvious problem with the rubber bits.  
On my model the vent to atmosphere seems to be just to the left of the opening.  I attached a length of hose to the aluminum pipe and blew gently.  No sign of obstruction there. I have not removed the tank and traced that line to the other end as yet. I removed a secondary fuel filter (Guglemeister from Italy) thinking it could have somehow blocked the intake to the fuel pump or otherwise caused this problem.  I found the filter pretty much as installed a number of fill-ups ago. I'll not replace it out of an abundance of caution.  
As an aside, before today I didn't fully appreciate how complex these fuel tanks are.  Their construction was certainly not simple or inexpensive!
Could this be a fuel pump problem?  The bike has 32 k miles on the clock and I believe the pump is original, although I did renew the fuel filter when I bought the machine 10 k miles ago.

brickrider2 wrote:Could this be a fuel pump problem? 

So it whooshes. Your moto runs well. If you are compelled by forces beyond your control to do something, do this. I performed this modification on my moto's cap and whooshes don't even register in my consciousness anymore. Of course, the effect of incipient deafness is always a possibility at my age.

O, the service bulletin section is full of little chores to satisfy the obsessive, like installing an extra ground wire to the temperature relay to cure some of its glitches, or routing a hose from the tank ceiling-style fuel return line outlet of later models to dump behind the fuel pump for slightly greater range and less noise at lower fuel volume. Think of the protection you'll give your pump then.

I should reveal that I didn't use an 8mm drill; I used a 7.9375 mm drill so there's that to consider.

Your bike will probably have a positive venting system as it most likely conforms to the CA smog rules so it is quite likely that in the same way a can of fuel that is part filled will build pressure if shaken then when left to sit the vapour will slowly condense back to liquid so maybe there was a momentary pressure build up in the tank due to the motion of the bike. I would not be too concerned about it unless you have problems with fuel delivery. Slight pressure will cause big problems with carbs but not with EFI.

The tank cap does not have anything to do with the venting.


The vent is inside the tank, near the top as it also acts as an over flow, pipe goes down through the tank and comes out the bottom. Any vacuum means this pipe is blocked, strimmer line or pipe cleaner pushed up from the bottom works but any crud then gets pushed into the tank. If you take off the tank cap your hand fits in and put a small glove piece over it to catch anything coming through.

92KK 84WW Olaf wrote:The tank cap does not have anything to do with the venting.

Apparently, some of BMW's engineers thought it did. That's why the service bulletin at the link in Reply #10 was issued. Probably most of them have retired by now and either realized the error of their ways or evolved into golf. Regardless, it's nice to have something to do.

Lack of gasoline in the tank couldn't have been the source of the engine dying.  It was well over one-half full.   Mulling over events of the recent past, I suppose I should mention another oddity.  Before this incident I had a Twilight Zone moment.  (Given my level of expertise with electrons, it's easy to have such moments.)  I pulled the bike into its parking spot and heard a noise at a time all should have been quiet.  It was a buzz I took to be the fuel pump.  I discovered that with the key in the ignition while the switch is off there came a soft buzz from the tank.  Remove the key, noise stops.  Insert key, noise resumes.  The next day I failed to duplicate that episode, so I dismissed it as possibly a moment one experiences when in the Twilight Years  .
On my warm up ride this morning the bike ran as it should.
With such few miles on this engine, I don't anticipate the fuel pump failing, but it must be a possibility.  Intermittent issues are fun -- not!
The idle speed on this machine has been on the low side since I first took it under my dubious care.  Today I consulted my Haynes book and set about raising the idle speed.  Haynes makes no special reference to K1100 engines differing from K100 engines in the adjustment procedure.  I found that turning the indicated adjuster really does little or nothing to change the idle speed.  Is idle speed controlled by the computer on K1100 engines?

Your soft buzz from the tank could be from a relay in the electrical box under the tank, the buzz is likely to sound like its from the tank. The relays can go faulty and chatter and the ABS relay is high on the suspect list. So too is the flasher relay, had it on one of my Ks.

brickrider2 wrote: Haynes makes no special reference to K1100 engines differing from K100 engines in the adjustment procedure.

Which Haynes manual? Which K100 engines—2V or 4V? Here's BMW's K1100 manual.
You probably just experienced the effects a dodgy electrical connection, relay or a star-misalignment. Clean the fuel pump connector. Clean the ignition switch connector.

92KK 84WW Olaf wrote:The tank cap does not have anything to do with the venting.

Just to end my obsession with this thread, you're correct, Olaf. In the EU, the tank cap has no venting; however, in the USA it does. That is the market to which the service bulletin is addressed and that's why I made the modification to my moto's cap. brickrider 2's moto is likely to be a US version, also.

I haven't noticed whooshing causing widespread panic over here but I suppose an occasional incident of vapor lock is possible.

I have ridden about 200 miles since my "whoosh" moment without further problems, so I am putting it all down to misalignment of the stars.  Thanks for posting the BMW shop manual.  If I understood it correctly, the idle speed is to be adjusted with the air bleed screws.  This is not the procedure described in the Haynes manual -- a substantial vol. (2002) which addresses the earliest of K-bikes, with a supplement especially for the 8-valve models in later years.  When next I have the fairing panel off I'll attend to those air bleeds to attempt to raise the idle speed. 
BTW, my cap does have the vent hole, as it was first sold here in the US (Wisconsin, I believe).  I didn't measure the hole, but it looks as if it was never enlarged per the factory bulletin.

I have ridden about 200 miles since my "whoosh" moment without further problems, so I am putting it all down to misalignment of the stars.  Thanks for posting the BMW shop manual.  If I understood it correctly, the idle speed is to be adjusted with the air bleed screws.  This is not the procedure described in the Haynes manual -- a substantial vol. (2002) which addresses the earliest of K-bikes, with a supplement especially for the 8-valve models in later years.  When next I have the fairing panel off I'll attend to those air bleeds to attempt to raise the idle speed. 
BTW, my cap does have the vent hole, as it was first sold here in the US (Wisconsin, I believe).  I didn't measure the hole, but it looks as if it was never enlarged per the factory bulletin.

brickrider2 wrote:I didn't measure the hole, but it looks as if it was never enlarged per the factory bulletin.

I doubt there was ever a production change to those caps. Vent modification doesn't seem to have been part of a recall either. It was all left up either to dealers as a way to satisfy customers if they complained, or to bystanders like me with a service bulletin, a drill and idle time available.

Laitch wrote:

brickrider2 wrote:I didn't measure the hole, but it looks as if it was never enlarged per the factory bulletin.

I doubt there was ever a production change to those caps. Vent modification doesn't seem to have been part of a recall either. It was all left up either to dealers as a way to satisfy customers if they complained, or to bystanders like me with a service bulletin, a drill and idle time available.

I just toss the flappers to get an extra 20 miles of range out of a fill up.  Easier to see inside the tank as a bonus.  As far as I know, gas stations don't have two different size nozzles for gasoline anymore.

Point-Seven-five wrote:. . . toss the flappers . . .

Working up a dance tune with that title on my accordion asap. Inspiring!