5 replies [Last post]
redavide's picture
Joined: 12/04/2007
Posts: 80

R69 was running fine. One day it suddenly wouldn't start. Took out the plugs and laid them on the cylinders and kicked it over in the dark. Only a very small, faint, weak white spark appears at both plugs.

Any suggestions as to next thing I should check?

Thanks in advance . . . . .

schrader7032's picture
VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6744
Check that the magneto is

Check that the magneto is timed right. If it's slipped from alignment, you'll get a weak spark. Could also be a failing coil. Not sure really how to check a coil other than to swap in a known good one.


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

312Icarus's picture
Joined: 07/15/2016
Posts: 409
Don’t forget the obvious,

Don’t forget the obvious, consider a pair of new plugs. That said, spark is pretty hard to see sometimes.


skyler.robbins's picture
VBMWMO #9513
Joined: 09/22/2018
Posts: 56
Clean your points and check

Clean your points and check gap...

FL54's picture
Joined: 08/12/2018
Posts: 64
Somewhat similar thing

Somewhat similar thing happened with my R50. Started it up, ran for about 10 seconds and died. However, when I pulled the plugs there was no spark. Troubleshooting the issue, I discovered that the nylon rubbing block on the points was worn down flat. Cam couldn't open points. New set of points and cam we'll lubed and problem solved. Mental note to check cam occasionally to insure lubrication.

johnpst's picture
Joined: 03/22/2016
Posts: 74
Ignition SYSTEM


You will find I always have the same answers on this site. We cannot troubleshoot through posts unless it's just an obvious issue.

The ignition is a system. You need to inspect all of the above and then some to insure it is working correctly. It's all pretty easy but, requires some time and some instruction. Here's a link to what may be considered one of the most comprehensive documents on the topic. https://www.snafu.org/restore/uandm_bmw_v1.pdf. You'll find it all over this site.

Kurt, Icarus, and Skyler are rightly leading you toward each component. I'm a big fan of insuring the whole system is working.

If you follow anyone who had these or other magneto ignition systems in the 50's and 60's, they had a tool pouch, a set of points, and point file, feeler gauges, and a condenser in the tool kit. We were the ones riding our bikes not calling our wives to bring the pickup truck.

Things to check:

1. Spark plugs. Just buy new ones. Troubleshooting them can be troublesome and cannot take heating into consideration so, just have spares on hand. The good news is, your's work so you seem to be ok but, that can change while heating up. Have spares.

2. Condensers are cheap. Have a spare. They can leak (electrically) causing weak or no spark.

3. Points; have files on hand and keep a set of spare points. Paper abrasive is not recommended because it can round the contact but, will do in a pinch to clean the contacts. The insulation can become contaminated and leak to ground causing weak or intermittent spark.

4. Coil. If yours is original, replace it. Single best thing you can do to restore power and startup reliability. Coils are susceptible to insulation breakdown over the years. The reported leading indication of coil failure is exactly what you are reporting. Starting, running, then shutting down with hard starting until it cools down. Weak spark is typically observed. Replace it. Also, there are two air gap conductors under the plug wire terminals. Make sure they are ~11mm. Too close and the spark will jump that gap instead of the spark plugs. Too far away and the coil will overheat over time.

5. I leave magneto and point timing until later in this post because I presume if it was running then not, it's probably darn close. I do recommend you verify timing of the magneto is correct (the whole system thing). This allows the absolutely highest power spark to be delivered at the moment of ignition. Doesn't hurt to verify the armature is well magnetized. If a 6" adjustable will stick to it with a little fiddling, you're good.

6. Plug wires are always good to replace every 5 or so years. At the very least, look closely at them to insure the insulation is not broken down. Newer wires are just better made that 50's/60's wires.

If the SYSTEM is correct, the ignition will be reliable. Good luck. We're all behind you. Let us know if you have any questions.



55 - R50, 06-R1200RT, 96-M900, 10-TU250x

Comment viewing options

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