Help Required - Bike Not Running Properly

Mark Douglas · 03-04-2001, 12:24 AM

On the way home on Thursday night, my 11S started running badly on decceleration or partial throttle openings. It's fine if you crack the throttle open but as soon as you start to deccelerate, it sounds, and feels, as if it's running on one and a bit cylinders. It's not as bad as a full cylinder missing as I removed the electrics to each fuel injector in turn and it got worse both times so both cylinders are contributing something.

Trouble is - I use the bike daily and the dealer can't fit me in until the 14th! (!st March is date for new registration marks in the UK so their workshop is backed up getting new customer bikes out.

I strongly suspect a leak in the intake plumbing, downstream of the throttle bodies. My reasoning is that under decceleration/partial throttle, the level of vacuum is high. On full throttle, vacuum is nil. If there is a leak in the intake arrangement, then it would cause problems when the vacuum was high enough to draw air in through the leak.

Any thoughts or similar experiences. I may get a chance to go out and have a poke around today but I've got a stinking cold and its 0 degrees C outside (32F)!

I've only had the bike for 8-10 weeks and its been absolutely fine for the 900 kmiles I've covered so far. This problem came clean out of the blue on Thursday.

tvrla · 03-04-2001, 08:03 AM

Mark,

I haven't had it happen to me, but I've heard that garbage can lodge on the throttle pulley wheel. I'd bet that's what happened to you. Just open the throttle and make sure nothing is preventing the throttle cable from seating in the groove.

Terry

Bob Hancock · 03-04-2001, 08:38 AM

Mark,
I don't know if Brit bikes have the charcoal cannister for evaporative emissions, but it can cause symptoms like this. If you have it, just pull the rubber tubes off the bottom of each throttle body and go for a ride. The fix will be obvious if this is causing the problem.
HTH,
Bob Hancock
'99R11S
'01 996

Mark Douglas · 03-04-2001, 10:53 AM

No carbon cannister on UK bikes.

I did make it out to the garage this afternoon - no inlet leaks, valve clearances spot on, new spark plugs fitted, motronic fuse removed to clear error codes. And it still runs poorly.

I didn't interfere with the TPS but I did measure the rest voltage - 0.335V. Brass throttle screws were between 3/4 and 1/14 out from fully in. I don't have vacuum gauges so I couldn't go much further. Very frustrating - it ran great up until Thursday and nothing has happened to change things - same old 32 mile round trip every day.

I did notice that I have nothing in the Motronic Coded Plug position in the left hand relay box. Is this right?

03-04-2001, 12:10 PM

Have you checked the rubber bungs that seal the take off points for vacuum guage fitment? I noticed these were perished on my bike but replaced them before they could cause trouble.

Andy

brad black · 03-04-2001, 11:37 PM

check to see if both throttle cables are sitting in their screw adj on the throttle bodies. if the pop out they really screw things up.

brad

doberman · 03-05-2001, 12:29 AM

I had the same problem with mine.
The BMW dealer changed everything, and it did not help.
I took it to my favorite (non. BMW) dealer, and he syncronized the injection.
Now it is spot on.

CarlosT · 03-05-2001, 06:41 AM

Bananas in the cans?

lennie · 03-06-2001, 02:23 AM

I have to agree with Brad. I have had this happen on a couple of occasions while getting the tank off/on where the cable has snagged and jumped up out of the retainer.

The bike sounds really sick and very rough.

it may not be the problem but is easily overlooked.

Regards,

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LENNIE