My R100GS is not running so well at the moment and I need some ideas on what might be causing the problem.
The bike idles and accelerates fine, but when I get moving and hold it in the low to mid rev range it runs very rough. The right hand carb is running too rich (sooted spark plug and exhaust) but I can't seem to solve this by adjusting the mixture screw.
I overhauled the carbs with new O rings a short while ago, but not the diaphragms as they seem fine.
I balance the carbs by ear because I'm on the road and don't carry a 'carbtune' or similar, so they may not be perfectly balanced. However, I also balance my girlfriend's R80ST by ear and it runs like a dream...
Does anyone have a good idea what might be wrong? I'm leaning towards the float needle being worn.
Harvey
www.chasingthesun.org

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Hi,

I don't know the BMW very well (actualy not at all), but I guess the mid-range is not affected by the mixture-screw. This screww usually covers 1/8 part of the carb-opening.
The rest is up to the needle and main-jet, so your idea about changing the needle could be a good one.
It could also be the jet itself, I would always change them as a pair. You could try putting the needle a click lower.

Good luck

Maarten

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I'm no expert - but from what you say it could be a problem with one of the jets that's in use for your throttle setting you're having problems with.

My Haynes manual says that "1/8 throttle setting is controlled by the pilot, 1/8 to 1/4 by the throttle cutaway, 1/4 to 3/4 by the needle position and from 3/4 to full by the size of the main jet.

From your description it sounds like the problem is occuring at the point when needle position is critical. Perhaps this needs investigating and making sure both needles are set-up correctly and aren't worn (they go oval after high mileage)- I seem to remember that if they are removed, the clips that hold them in place need to be put back in the correct groove for both carbs.

Haynes also says the following (under "Poor running or lack of power at high speeds"):

To check that the main jet isn't blocked. Water in the fuel can also be a problem. Condensation inside the tank can gradually create enough water that'll sink to the bottom of the tank and cause running problems (unlikely though). Air bleed holes could be blocked. Check the fuel hoses for kinks or blockages or the diaphragn could be split (hold it up to the light).

Hope some of this helps - most of these suggestions come out of Haynes... Perhaps you have a manual and have already tried these things? Good luck - I know from personal experience how frustrating carb problems can be - it might be worth getting them checked out with gauges, if this is possible? Diagnostic equipment really helps solve these sort of problems I think...

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Fuzzy Duck
(I'm quackers about bikes)

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Fuzzy Duck
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Hi Harvey, Cleen out your carb as much as possable without taking them off the bike.
Check your diaphram and the jet needle.
Sometimes the jet needle clips can wear a slot in between the clip positions.
I am not sure which carbs you have. some jet needles go in from the bottom of the slide and you turn-push-pull to adjust them, some go in from the top of the slide under a screw in the center tube of the slide. I think the needle jet is the mid-range mixture
Let us know what you find. Good luck. John

Check your floats and float needles.

New floats weigh in at 12 to 12.5 grams. The rubber tip of the float needle may be getting hard and not sealing as well.

Correct float level adjustment is achieved when the floats are parallel to the mating surface of the float bowls on the carbs, at which point, the needles should be sealing.

Did you do a quick overhaul, or did you take the carbs apart completely?

Did you clean the area of the atomizer and needle jet. These items are held in place by the main jet holder. Notee that thye are difficult to install unless the carb is upside down. This area can really get clogged.

Is one choke plate not returning to the "off" position. Rememeber, these are pulled back by springs that may be weak and if the shaft is sticking, you are driving with the choke "on". Check by manually pushing down on the levers.

Let us know what the problem and solution was.

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Alex

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hi harvey,

i dont know if you have fixed your 'running rough' problem in the meantime. but if you dont find anything about the carbs, here's another hint:

i'm not sure what kind of ignition your 89 r100 has, but it might be possible, that the fixing between the camshaft and that part, that tells your ignition to ignite (it depends on model and year but should be a so called Hall-Geber (in german)), is somewhat worn out. with the result that also both ignition-signals are still exactly 180 deg. apart, one is little too late and the other too early.

if you havent fixed the problem yet send me a mail with information about your ignition-system, and we get into it.

long may you run
gerd

Chaps,
Many thanks for all the advice. I tried various different things and eventually narrowed it down when the HT lead failed on the way back from the Tibetan border! A new lead seems to have solved the problem, but I need to get out of Bangkok before I can really tell.
Harvey

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no pipe, no slippers
www.chasingthesun.org

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no pipe, no slippers
www.chasingthesun.org