R100GS fault. Help!

[Chris8]

Hiya any advice on this fault appreciated. My R100GS idles fast when hot. I am convinced it is an electrical fault as when you switch the main lights on, the idle speed drops down to normal 1200rpm or so (from 2000-2100rpm). The red charge warning light sometiomes comes on to... this gets fixed by removing the tank and "fiddling" with the electric gizmos underneath. Don't know if this is related. Any way this doesn't seem to fix the fast idle fault.
I am not an electritcian so any advice folkies familiar with the R100GS can give appreciated.
Having subscribed to o/s BMW websites it looks like lots of R100GS owners replace their diode board... but what the f. is that???
Cheers
Chris

[Kiwi]

Hi Chris8
Where are you based? Maybe I can have a look at your baby

Kiwi

[Chris8]

Thanks for the offer but I'm in the Wgton area. Bikes still entirely useable but it's just not running right re the idling.

[Kiwi]

Hi Chris,

Diode board???? Sounds more like a bad contact. What year is you baby?
Kiwi

[Chris8]

Thanks for your trouble.... the bike is a 1992 model, black and yellow bumblebee, done just under 50k/km. Thought this fault might be a congenital BMW fault that someone may recognise. Some of the o/s web sites feature common things that go wrong with the R 100 GS, owners often replace their "diode board" thingy with after market ones. Could be something else though.

www.micapeak.com/reg/bikes/R100GS/

Chris

[Kiwi]

Hi Chris,
How is your bike? I have the same model but never ever problems with the electric – I travelled 3 times through the desert (Sahara) on my R100 GS and 5 times with my 80 GS.
Have a look at all the plugs. If you have a mate with the same mode, change the black box and see what’s happen.

See Ya
Kiwi

[Chris8]

tHANKS muchly Kiwi, but very little progress so far... the bike has not been touched this week. Interesting the advice from BMW-GS mailing list on micapeak.com.....various comments from around the world none of which say the electrics are at fault. Most say check valve clearance, carb synchro, air leakage on boots between carb & head. I'll check these out anyway. The plugs have recently been replaced anyway.
Tell me, when checking valve clearance is it necessary to check tourque settings on head bolts as well, as the Haynes manual advises??
Chris

[Kiwi]

Hi Chris,

It is not necessary to check the torque setting on head bolts when you checking the valve clearance. I do it after 10.000 km or once a year.
Good luck

Kiwi

[Enn]

hi ya i got the same prob (81 r100rs) all i could find is carb sync, poss leaning out when hot.
cheers enn.

[Paul in NZ]

Mate I'm not really up with beemers... BUT...

I know the older ones used the same weedy Bosch charging system used on Guzzi's for yonks.

The diode board will be the rectifier (convers AC from the alternator to DC for the bikes electrical system. Unlikely to cause a high idle speed?

The charge light is vital. If it blows or is disconnected, your system will not be making any power at all. the exciter current for the alternator runs through this cct so if you turn the key on and the light does not come on, you have a problem.

Regardless of that, if it has carbs, the idle speed will be set by mechanical adjustment. Turning the light on will add load to the alternator and slow it down though. (not usually much though)

I'd check you throttle cables are not snagged on something or the outer pulled out of the twist grip or summat. Then see if the carb slide responds to the idle adjuster screw. (if you don't know what that is, get it checked at a shop, buy a book on carb or search the web)

If it has fuel injection your whole bike if totally fucked and I would sell it to the nearest Guzzi owner for $5 who will then dispose of it in a dignified fashion..

Ah hem

Paul N

[Milky]

hi ya i got the same prob (81 r100rs) all i could find is carb sync, poss leaning out when hot.
cheers enn.

Suggestions:
check float levels
synchronise carbs
set idle when hot

Do you have the same problem with the lights?

[bmwr690s]

The auto advance and hall effect mechanism js in what is commonally known as the bean can under the front cover of the motor. It is not uncommon for the advance mechanis to sieze on itself and not auto matically retard when you close the throttle. The symptom for this is a high idle speed. It can be corrected by removing the B C unit and carefully dismantling it and freeing up the mechanism. There is a detailed explanation of how to do this on the Airhead site written by snowbum.
The airhead site has a wealth of info for BMW owners.
I would only do this after you have exhausted all other avenues ie. balancing the carbs and setting the idle with the engine running operating temperature.
The only anomally for me that doesn't fit is when you switch on the headlight and the idle comes down.
Good luck,
Steve.

[Enn]

Suggestions:
check float levels
synchronise carbs
set idle when hot

Do you have the same problem with the lights?

no forgot that one no probs there

[Ixion]

Are you sure that it's not the other way round? That the idle speed is set high because some one didnt want to have to use choke when cold - or maybe it was set thus when cold . 1200 rpm, when cold, that would then go up to about 2000 when hot. The slowing down when you turn the lights on may be totally unrelated, due to the extra load on the alternator pulling back the revs.

If its idling to fast the logical thing seems to be to turn back the idling adjusters until it idles nicely when warm . Then presumably it wont idle when cold. So adjust the choke/cold running adjustments until it does ??

[Posh Tourer :P]

Having the idle drop when you turn on the lights suggests either your battery is screwed, or your charging system is (Remember TS's RG Milky?). Battery is easiest to check, then try look at the charging system. This is all academic anyway, as the original post was in 2002. However, it is nice to see the old boxer owners coming out of the woodwork, even if the only thing we talk about is faults with our bikes :P