BMW R90 starting issues

[Nilsey]

I think i fried my diode board. Would that be enough to make the bike not start anymore or is that just to convert the AC from the alternator to DC to charge the battery?

When i press teh starter button it just clicks or whirrs, doesn't seem to engage the engine.

i'm trying to daignose this but not really finding a useful path, any ideas would be appreciated.

[Nilsey]

correction, i just tested the diode board and it tests fine. http://www.frankhams.freeserve.co.uk/testing_the_diode_board.htm

so, whats the next suspect?

[jds-MothSteward]

That kind of starter behavior is an indicator of a weak battery. Have you checked the battery?

[Nilsey]

you were right i was able to jumpstart it from my car.

i must have had a bad connection when i tried that yesterday.

thanks

Nils

[Nilsey]

This raises anoterh question - on some bikes i've read that hooking up a charger to teh battery while the battery is still connected to teh bike can result in damage to the rectifier/voltage regulator.

does anyone know if that is teh case with an airhead BMW?

can i hook the charger  (or battery tender) straight up or do i need to disconnect the bikes ground every time?

[Joe Block]

One of the known slight ( in deference to BMW fanatics) weaknesses of 1970's BMW airheads is their charging system and expensive stock weird battery size and battery life.
In order: check battery condition, clean all electrical connections (most are under the tank), check starter relay.
It is OK and recommended to hook up a good quality battery charger in line. BMW has (or used to) have an accessory female plug available to fit and you can use that to plug in a charger with the correct male lead.
I recommend OptiMates (http://www.smartchargers.com). You can also now get high quality maintenance free batteries that will be a satisfactory close fit, I use a Panasonic LC-X1228P.