R90S Starter operable when engine running

[motorradfanatiker]

On my 74 R90S the starter will run when the engine is running in neutral and the button is pushed.

This is a problem for me because I have a wide tank bag that bumps the button and grinds the starter when I’m backing up the bike. I have been thinking of installing some kind of additional cutout but I’m not sure the best way to do it. Maybe just a manual switch to cutout the starter when using the tankbag. Any ideas would be appreciated.

[srankin]

Probably the best way to solve the problem is breaking into the Starter button switch circuit and installing a on/off switch of some kind. Or fabricate a shield for over the button? Or move the button? Good luck, St.

[schrader7032]

I guess we went through this... But why does the starter engage at all when the engine is running??? I'm not going to try it on my /7, but it just strikes me as odd that that can happen.

[motorradfanatiker]

Has anyone tried using a /5 starter relay on an R90S or other /6 to have the restart protection? It seems funny that BMW would have the restart protection on the earlier /5 and remove it from the /6. Maybe because there could be some problems with the /5 relay when the battery was low or on cold mornings.

Another solution I’m considering is to install a normally closed relay into the starter button wire and switching it with the headlight voltage. This would allow starting with the headlight turned off, and prevent starting with the headlight on. This may be cleaner than a manually operated switch.

[schrader7032]

My /7 has a stock light cut-out relay in the starter circuit.

[motorradfanatiker]

My /7 has a stock light cut-out relay in the starter circuit.

From what I’ve read from ‘78 onwards most airheads had a rely to turn off the headlight when the starter is running. These bikes had the mandatory headlight always on setup. This is different from restart protection like the /5 had that prevents the starter from engaging while the engine is running. Does your /7 have the restart protection?

[schrader7032]

I don't know, Jerry. I can't read the diagrams well enough to see if there's something there. I'm not familiar with the /5 circuits either.

[motorradfanatiker]

My solution to the tankbag grinding starter problem:

I installed a normally closed relay into the starter button circuit, which is opened by power from the running lights. Now it will only start while the switch is in position 3. Positions 1 & 2 have no ignition on. Positions 3 & 4 have the running lights on. So when I’m backing out of a parking space with the engine running and lights on (ready to go), the starter will not work when the button hits my tankbag.

It was an easy install, no wire cutting. I just made 3 short jumpers and plugged them into the relay as follows:

Relay terminal 30 - remove one of the Brown/Yellow wires from the terminal board section 85, Brown/Yellow from starter button

Relay terminal 87a - jumper to section 85 where you unplugged the Brown/Yellow wire

Relay terminal 85 - jumper to a free section 58 terminal Gray/Black -running lights

Relay terminal 86 - jumper to a free section 31 terminal Brown - ground