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  #1  
Old 6 May 2009
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hesitation on acceleration 1996 1100GS

I have a maintenance question which I have asked many people and have not been able to get a good response to, so here it is:
I have a 1996 1100 BMW GS. It hesitates when I give it throttle. This started only when I put the motor under a lot of stress, I.E. opening it up from 80 to 90 with two people on and sidebags to add to the wind drag. Now it does it all the time. I can’t even get past two miles an hour unless I gently give it the most miniscule amount of gas. It took about a month to get to this point.
I thought I needed to gap the valves, so I did that, and it worked, for about 600 miles. Now I am back where I started. The bike has been sitting now more than a year.
This all started within a few thousand miles of me giving the bike a major service. I rode this bike to Panama, with someone on the back and also on many dirt roads, which needless to say did a lot of damage. I continued driving it for about a year after I returned from the trip, until the master cylinder started leaking brake fluid on my hand. I changed that, replaced the right side head gasket which was leaking, replaced the air box which was broken(maybe something got into the fuel injectors before I did the replacement), and quite a bit of other things which should be unrelated, (a little electrical work, etc.). Like I said the bike ran well for about 1-2 thousand miles after this service.
What could this be? I can’t keep gapping the valves every 600 miles. Any Ideas?
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Old 6 May 2009
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Does this hesitating equate the Bing hestiation on the 2-valved?

On the 1100 you have:
- a butterflyvalve
- fuel injection
- air mass(?) gadget adjusting the amount of fuel injected to correspond with the amount of air.
What you describe is a probable malfunction in the balance between these mixture regulating parts, but I still wonder about the following:...

You say that you have noticed that adjusting the valves corrects the problem. You did not say what play you did find and what play you set the valves at.
This phenomena should -not- be able to cause the problem you describe...

What colour did you say your plugs have, and how does the electrodes look?

You did not say if you have tested the compression. What is the current compression in your barrells?

You did not say that you have tested the fuel injectors. Do they produces the correct "spray and spread"?
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  #3  
Old 7 May 2009
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synchronised throttle bodies?

could your throttle bodies be out of synch? i happens fairly easily, even as a result of uneven stretching of the throttle cables, which are of uneven length and therefore susceptible to this (have you replaced them?)

even a little bit of dust or crap between the cable-ends and the adjusters at the throttle bodies will do it.

ahh, yes, i remember the time, long ago, when my R11GS would take off without throttle...

cheers,
andy.
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Old 8 May 2009
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desert dweller I have synced the throttle bodies with a mercury vacuum gauge. They read differently at idle and at about 2k rpm. I synced them at 2K. I am on about my sixth set of throttle cables as they just seem to wear out from all the grit from the dirt road getting in there.
DC lindberg, I live in a condo complex and am not allowed to work on the bike here, so I was trying to get an indea of what to try, as I am going to have to do the work at a friends house and try to do it as quick as possible. I will first try adjusting the air/fuel mixture screw and while I do that I will pull the plugs and check the compression. If that doesn't fix it I will post again with updated details.
As for the fuel injectors, how do I check them?
When I checked the spacing on the valves, 1 side was fine, and 1 of the other valves on the opposite cylinder was out, and the other three were fine(I think). I set the distance to the amount spec'd in my miantainence book. I think thats in storage but I'll post when I have the info.
Thank you both
Dylan
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  #5  
Old 8 May 2009
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DW, if adjusting the valves solved the problem, albeit temporarily, it's possible that you have a loose connector somewhere in the system and you inadvertently, and temporarily, fixed the problem simply by reconnecting a poor fitting connector.

Whilst adjusting the valves you will likely have undone, and done up, various connectors. Think back as to which ones you did undo and check these for good fit. You could even do try wiggling each connector in turn whilst twisting the throttle in neutral to see if it affects the hesitation.

Just a thought, and a cheap, quick and easy diagnosis.

Garry from Oz.
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Old 8 May 2009
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Quote:
Originally Posted by dylanwilliams View Post
I live in a condo complex and am not allowed to work on the bike here, so I was trying to get an indea of what to try, as I am going to have to do the work at a friends house and try to do it as quick as possible. I will first try adjusting the air/fuel mixture screw and while I do that I will pull the plugs and check the compression. If that doesn't fix it I will post again with updated details.

As for the fuel injectors, how do I check them?

When I checked the spacing on the valves, 1 side was fine, and 1 of the other valves on the opposite cylinder was out, and the other three were fine(I think).
Dylan
Someone who have tested injectors should reply to that question. I think the procedure is described in Haynes or Clymer Workshop manual - it sure is in VW workshop manuals for the Type 2 and 4 busses. Something about using a sheat of paper to "fire" at. The spread and intensity will be evident on the paper. But, to get the best advice and techical aid - it is better if someone who have done this test describes the correct procedure.

If all you lost was the play on one valve - it should not have this huge effect on power and accelleration... could it be caused by that catalytic gadget?

There is something going on that hampers either the injection of fuel or entrance of air... just like the throttel hesitation in vaccum carbs like Bing...
The cause must be so simple that it is overlooked!

Compression will tell you if the rings are bad or a valve is leaking. If the piston rings are worn-out you will encouter this weird phenomena that you describe - happened on my Suzuki when the compression went below 7kg, and at 6kg the bike was not as funny to drive even though it could reach and cruze at 100-110mph.
Friend of mine took his R90/6 to FIMA in Tunis. After visiting Sahara his engine had transformed from a 4-stroke to a "2-stroke" (consuming oil like 1L/100km...). You did not say you have an excessive oil-consumption.
Hence - the cause must be simple...
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  #7  
Old 13 May 2009
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Have you replaced the air filter?

If the fuel filter is clogged, it can cause a serious lack of power all through the rev range, it should be changed at 24,000 mile intervals. Slightly tricky job, don't overtighten the 5mm studs.

Failing Hall Sensor can also lead to poor running, it's located behind the lower alternator belt pulley.
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