R80RT Stalling Problem - Help!

[R80rider]

Excellent information!  Tha fuel cap is funky, so I am going to try this today.  I also have an 87 so will use the fuel cap off that but still back it off per your suggestion.

Thanks and I will let you know!!

Bill

[R80rider]

Monte Miller: Eureka, Sir!!!!!

I just got back from a 70 mile ride on the R80RT.  I didn't take your advice word for word, but since I have 2 R80s, I swapped out the gas cap, started the cycle up and ran her faster, harder, higher revs and even left her idling while I stopped for a coke.  

Not one miss, backfire or stall!!!

She ran like a total dream!!!!

And, yes, I am happy.  

So when I got back, I inspected the "faulty" gas cap, and sure enough, some yahoo of a PO had taken silicon sealer and ran a bead around where the o-ring and gasket should be.  Since this was not a problem on other rides, but originally manifested when it was very hot, I have 2 theories I would like to present for everyones perusal.  The may be stand-alone or a marriage, but it would be nice to feel like I know what caused it (besides the obvious PO with his tube of silicon).

1.  When the silicon was exposed to the prolonged heat, it naturally expanded.  This led to it blocking the vent port in the top of the tank.

2. Natural vibration and gravity caused the silicon to slip from its original position and this in turn, blocked the vent port.

As always, I am open to other ideas, so lay them on me.

Case closed?

Ultimately, I am extremely happy that it was NOT the coil and even more so that it was NOT the beancan.

As always, I appreciate all the input, ideas and experience!!

And, Monte Miller, if you are a beer drinker, I owe you a case.  Thank you!

Bill

[montmil]

Monte Miller: Eureka, Sir!!!!!...
And, Monte Miller, if you are a beer drinker, I owe you a case.  Thank you! Bill

Glad it worked out. And you can drop the "sir" stuff... that was my dad.
Too bad I didn't check this thread before I went out this afternoon and bought a case of, what else, Miller Lite.  [smiley=beerchug.gif]

[R80rider]

I don't know where the sir came from as I am probably older than you.  

You know, of course, upon further reflection, it is really embarassing to have not been able to figure out that my fuel cap was bad.  

I took a couple snaps of the good vs the bad cap.  The photos turned out with a blue tint and I am not sure why, but here they are:

http://picasaweb.google.com/bill.cochran/Fuelcap

Does anybody have any idea what would compel someone use silicon sealer on one of these fuel caps?  I mean, what symptom(s) might they have been attempting to address?

Also, after examing the photos, does anyone see any reason why I cannot remove the silicon and purchase the correct parts to get this fuel cap back to specs?  

As you can guess the caps are not cheap and then their is the keying to deal with.

Parts Information from MAX BMW:

http://picasaweb.google.com/bill.cochran/Fuelcap/photo#5222625045082938514

Bill

[Justin B.]

I don't know whether the silicone was causing your venting issue or not as it looks like it was just supplementing the seal.  I believe the tank vents through those 4 holes in the bottom and something is likely clogged up/frozen inside there.  The rubber seal and the black plastic trim ring are still available.

But, if the silicone was sealing the plastic trim ring to the tank then that may be altogether something else as I think that is where it breaths through.

[not-so-fast-ed]

Speaking of keying,  My key fits everything BUT the fuel cap.  PO must have replaced it (?)
Any idea if the cap could be reset to my key?
Ed

 :-/

[montmil]

I don't know where the sir came from as I am probably older than you. You know, of course, upon further reflection, it is really embarassing to have not been able to figure out that my fuel cap was bad. I took a couple snaps of the good vs the bad cap. Does anybody have any idea what would compel someone use silicon sealer on one of these fuel caps?  I mean, what symptom(s) might they have been attempting to address? Also, after examing the photos, does anyone see any reason why I cannot remove the silicon and purchase the correct parts to get this fuel cap back to specs? As you can guess the caps are not cheap and then their is the keying to deal with. Bill

Here's my original cap. Key lock drilled then back filled with epoxy.  DIY cork gaskets -most likely to prevent fuel sloshing out when riding with the cap unscrewed. Split rubber trim ring, too. Nasty looking.





I bought a very nice replacement cap, complete with gaskets, from these guys for half price. No key for the lock but no nasty cap either. Works for me.  BTW, Bill, I'm 61... sir.  8-)

http://re-psycle.com/

[Justin B.]

R80, I don't think silicone will expand with heat but I do remember it gets soft and swells a bit with constant/prolonged gas exposure.  I had a '73 Honda CB450 with a leaky seam once upon a time and I tried silicone as an emergency quick-fix until I could properly solder the leak.  It held up for a few hours then got soft and started leaking...

[R80rider]

Hi Justin,

That makes sense.  I have not received any real answer to my question about buying a new ring and gasket for this cap.  I see no reason to purchase a whole new or used one when it seems to me that removing the silicon and rehabilitating the current cap with the original parts which are only aroud 10 bucks would not be the recommended approach?

Any and all comments would be appreciated.  Pics of the current cap are a few posts up in a link.

Thanks!

[Justin B.]

I would give it a try as you really don't have anything to loose...  If it still doesn't vent then save y6our new ring and gasket for futures...

[Yikes]

I have been living with a non-venting fuel cap since I got my bike last fall.  It only took me about 5 months to figure out what was causing the mystery stalling problem.  Like montmil’s cap, mine had the lock guts removed and filled with epoxy.  Only my PO had also epoxied a neat little BMW medallion over the filled hole and being clueless about what the cap was supposed to look like, I thought it was fine.  It was only after reading about venting problems here on the Forum and looking at the parts fiches did I realize that there was supposed to be a key and lock mechanism where my little BMW badge is.  Needless to say, the cap has the venting qualities of a solid rubber stopper.  
So, with a little bit of newfound insight and nothing to lose I pulled the badge off and drilled out as much of the epoxy goo as I could get at.   In tinkering with the cap, I could see that there are holes on the side of the cap located just above the level where the rubber seal sits.  You need to pull the flat plastic ring off to see these holes. I concluded that these holes are the venting “intake” somehow connected to an opening in the cap that is in turn connected to openings in the lower part of the cap below the seal.  I tried drilling into the center void where the lock mechanism had been, though the existing holes above and below the rubber seal, but was defeated by what must be the remaining hardened steel lock casing, still firmly sealed into the interior of the cap.  Nothing lost but a couple of small drill bits and a couple of hours.
Anyway, R80rider, I’d recommend you pull your cap and remove the ring and seal washer and take a look for those upper holes in the cap.  If those holes are gunked with silicone sealant and you can get get them open, that might fix your venting problem and you won’t have to buy another cap or continue to switch your one uncongested cap between your two bikes.
Good luck with it!

John M.

[Justin B.]

You may have nailed  it, John.  You can see in Monte's pic where the PO had actually epoxied the bottom vent holes shut!  Ain't no way that sucker'll vent...  Plugging the upper holes would pretty much accomplish the same thing.  

[R80rider]

Sorry, it has been so long, but I just now got around to swapping the bean cans between my '86 and '87 R80's after the '86 got to the point where it would not start at all.  Once swapped, the problem, without question, moved with the sender unit (bean can).

I will be sending the defective one to http://www.motoelekt.com/ignition.htm as recommended by several of you.

Thanks for all the help!!