RS Sputter/Weep

["Tom Brown" <tbrown@xxxxxxxxxxx>]

Rob:

Disclaimer: I'm doing this from memory.  I'm at a desk, not in my garage.
Don't have manuals etc. in front of me.

>at almost/completely warmed (4-5 bar) if you shut down the
throttle as if /or coming to a stop, it will more than
occasionally do this sputter where the bike will drop to a
few hundred revs very suddenly, enough so that the alternator
belt chirps, and come back up just as quickly. It is a rather,
shall we say, forceful sputter/ stutter.

>The bike has never done this before, and the only variable has been a
service (42K) done at the most reputable dealer in the SF bay area.
I'm NOT faulting them, but I know they're gonna want a minimum $85
investigation investment, and I don't want to go there...yet


42K is about the time that new cables should be considered.  If my bike were
doing this, I'd at least inspect the cables and their adjustment and for
sure I'd start over with 0=0 procedure and a throttle synch. procedure and
see if that helped.

Also, there is a circuit on the FI that prevents backfire when you shut down
the throttle completely.  In order for it to work, the voltage from the TPS
has to be below 0.400 volts.  If the TPS voltage is set too high, you can
get all kinds of goofy effects.    Usually the dealer doesn't change the TPS
settings for love or money.   I'd look for loose screws on the TPS, though,
just in case it moved on its own. Also, look for evidence of it being
changed.  An incompetent may have changed it, then, after being told "never
change that!" might have tried to put it back where he found it...something
like that, use your imagination.  Shirt Happens as they say in the laundry
business.   Hard to find good help these days.

A 0=0 will set the TPS right as well as the idle stop screws and Big Brass
Screws.

The throttle cables might be set too tight.  If this is the case, the
throttle stops will never hit the throttle stop screws when you close the
throttles.  Then you're depending on the cables to always stop at exactly
the same place, which never happens.   What happens instead is that shutting
down fast gives you a different effect from shutting down slowly.  Sometimes
the idle is in synch and sometimes not because the two sides don't respond
the same etc.

A 0=0 will set the idle stop screws, the cables and the Big Brass Screws.

If the bike is set too lean, it may do that idle hunting thing.  This is
usually because the Big Brass Screws are letting in too much bypass air.
Again, I'd just start from scratch, do 0=0 and reset everything right.

Even reputable shops sometimes get busy and have to let junior employees
work on more routine procedures.   This can happen especially during a busy
time...like spring.  Sometimes, an experienced employee will be in a hurry
or just get spring fever.  These bikes are not all digital yet and there's a
lot of hand work that goes into tuning them.  People are people and people
doing repetitive procedures will inevitibly mess up.   I'm sure it's not
quite as much "feast or famine" in CA bike shops as it is here in IL, but
spring is generally the busiest time for bike
shops everywhere.   Anything can happen.   They shouldn't charge $85 to
investigate a
problem with a tune up they just did.    They should apologize and do it
over for you.   Something is wrong.

>Also, the bike has twice puked from the rear drive vent; the first time
it had been outside in cold December weather while I was out of my house
for a remodel, drove it 30 miles, parked it in a garage and it puked out
the vent. Maybe, 25 cc's? Guessing, as it was on the tire and wheel.
Maybe 6 tablespoons. Next time, I'd ridden it about 60 miles, parked
it in the garage, and next day rolled it out to the driveway. By late
afternoon, it had puked up three times the previous amount?

>I was wondering if sitting outside (undercover) for that time in
December (RAINNY!!)
if perhaps something got into the rear drive vent. The plastic cover
seemed fine.

Check the level of the gearbox oil.  It could be overfilled.   Again the
work of a rookie at the dealer?   You unscrew the top filler bolt on the
rear end with bike on center stand.  Oil should be visible down in the hole,
but not up to the bolt or anything.   See a maintence manual for photos and
instructions.  I think even the little owners maintenance manual thing that
comes with the bike has this in it.

Was the oil a milky color?  This would indicate water contamination.    To
be safe, change the oil.  If any of it comes out looking strange, add new
non-synth gear oil (cheaper), then go for a long ride and change again.
That should get
it all out, but do it once more in another thousand to be sure.   The third
time, put your $20 per quart BMW synthetic in there.  Don't overfill.

Yet another reason could be a leaking trans seal.  The oil runs down the
driveshaft housing and overfills the rear end.  Ususally this leaks our the
rubber boot, but if the boot is really secure, it's got nowhere else to go
but out the gearbox vent.   This is a warranty issue and a reputable dealer
should take care of this without much bitching.  BMW definitely pays on this
one.  It's a well known defect on some Oilheads.  It was a problem on some
of the castings, which, when combined with one method of assembling the
seals to the engine, caused this leak to happen after a while.   BMW has
changed the casting and the seal.   They have a notice to dealers and the
dealer can grind off a bit of casting when they reassemble and it won't
happen again.   Also the new seal design is better.

- -TB
(Do my own tune-ups now.  Dealer does brake fluid changes on my servo brakes
and safety checks...that's it)

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