3 replies [Last post]
jimmymac
jimmymac's picture
 Offline
VBMWMO #7543
Joined: 04/22/2009
Posts: 6

Well I was having problems with my starter solenoid, so I replaced that and the starter. The issue I was having was the solenoid was locking the arm out so when I started the bike it sounded like I was just holding the starter button. Now, the engine will not start. It turns over, but I have no spark. One coil tested good with a multimeter, but the other does not. Does anyone have any suggestions? Pictures of how the coils are hooked up or a picture of how the diode board is supposed to be plugged in would be a huge help as well so I can double check that it I did that right :roll:
Thanks,
Jim

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6844
R75/6 Problems

For the diode board, try using this:

http://www.stephenbottcher.net/BMW/misc/ChargingSystem.jpg

It's listed as R80GS, but that shouldn't really matter too much. But in general, the diode board is part of the charging system, not the ignition system. Bikes will run with a bad diode board as long as there's a good battery in the system.

As for the coils, you should have a green/black wire coming into the +terminal on coil 1, a black jumper from the -terminal on coil 1 to the +terminal on coil 2, and a black wire that should run to the points.

Are you still running points? Is it possible that you've pinched the black wire where the engine front cover attaches? If that's the case, the coils won't work.

Put a voltmeter across the +terminal on the first coil and the engine case. Turn the ignition on but don't start the bike. Turn the engine by hand a few times. You should see 12v at the coil but it will go away and then 12v will come back. That's how the coils work...12v across both coils storing energy, then when the points open, the 12v disappears and the secondary windings in the coils collapse, giving the spark.

As for testing the coils, I would measure the resistance from one spark plug cap all the way over to the other spark plug cap. You should be in the 20K ohms range. You may have the 1K ohm plug caps, so it could be a little lower. Each coil should measure about 5K ohms across the primaries.

Let us know what you find.

Kurt in S.A.

__________________

Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

jimmymac
jimmymac's picture
 Offline
VBMWMO #7543
Joined: 04/22/2009
Posts: 6
R75/6 Problems

Thanks Kurt, it look like it was a pinched wire and the connector between the two coils. On the diode board, I think I might have put the single connector on the back (as compared to the 3 hole plug) in the wrong spot. I have it vertical, can anyone remember if theirs is hooked up to the vertical or horizontal post? It certainly tried to start, which is a great sign before is was just cranking. I broke a plastic connector on my petcock so I have to wait for that before if I know if it will stay running, but so far so good.
Jim

schrader7032
schrader7032's picture
 Offline
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6844
R75/6 Problems

Jim -

The two single spade connectors on the back of the diode board are electrically the same. Obviously, the 3-hole connector is different which gets the three wires from the alternator. BTW, if you still have the molded rubber plug for these three wires behind the diode board, you might want to consider keeping it very clean or changing to three separate wires. The molded plug has a tendency to capture and retain moisture, setting up corrosion. I found that on my /7. I got three wires from Rick at Motorrad Elektrik for replacements. They're easy enough I suppose to make yourself, but I felt more comfortable have the right gage and connectors from someone who does this all the time.

Kurt in S.A.

__________________

Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.