Boxerworks.com

Hiya all,

This is just a quick heads up for those that are still running (afflicted with?) breaker points equipped bikes, in particular the older, pre-bean can, models.

This issue may have been addressed somewhere else on the forum but i couldn't find any reference to it, so I thought i'd pass on our insight into the problem and how it was resolved.

The issue arose after a minor renovation of a 1978 R100S, ie new rings, gaskets, and seals etc, which was done mostly to address some oil weeping from hardened/worn seals. We also replaced the points.

The problem came when we started the engine. It was running somewhat roughly, to the extent of occasionally backfiring. Closer inspection (of the plugs) revealed the RHS didn't seem to be firing correctly... hmmm...

It was a bit of stumper and we spent some time (ie hours) troubleshooting. We checked/replaced coils, plugs, leads, fuel... etc etc. but no luck... several beers were called upon but even they didn't help.

On a (much) later date we tackled it again... we started with the basics (ie step by step setup from initial conditions).

While doing so we saw a potential problem: the advance/retard mechanism was shorting out on the points wiring lug (where the wire from the condenser connects to the points)... surely that shouldn't be happening!... so, we bent the lug over to give it some clearance from the a/r. Result: No more misfiring and/or backfire. Problem solved! We checked the old points and sure enough it's lug was similarly bent...

So, if you're still running points, it may be worth your while to check that you have sufficient clearance between the points wiring lug and the advance/retard unit. Otherwise, mysterious poor running is prolly guaranteed!

Good luck,

pete

That is interesting and we never saw it. I will try to take a look and see if I understand exactly what was shorting out.

Several times we saw the points wire short out from the metal standoff vibrate enough to touch the wire. It would sort of cut out at one rpm and of course not go higher. We just bent the tang away from the place it touched.

Pete: Does your 78 have the later style point set up? Sorta looks like the "bean can".

I had the same problem with the same slow diagnosis on my 1975 R90.

Garnet wrote:Pete: Does your 78 have the later style point set up? Sorta looks like the "bean can".

Nope, the '78 100S has the pre-bean can setup, ie points/advance mechanism attached to cam.

My '79 RS has the bean can. I'm unsure if the same issue could befall it...

Duane Ausherman wrote:That is interesting and we never saw it. I will try to take a look and see if I understand exactly what was shorting out.

Duane: It was shorting against the adv/ret weight pivot pin. When we turned the engine over by hand you could actually see the points terminal lug moving when the pin rubbed over it.

No way that could happen in the same way on a bean can model as the advance mechanism is buried well behind the points backplate and the condenser connection is external to the can.

I'm wondering if the shorting points weren't OEM and were some aftermarket "equivalent"\? If OEM that would be very disturbing!


Ken

barryh wrote:No way that could happen in the same way on a bean can model as the advance mechanism is buried well behind the points backplate and the condenser connection is external to the can.

It's been a while since I've been in there, so the above info is good to hear...

Ken in Oklahoma wrote:I'm wondering if the shorting points weren't OEM and were some aftermarket "equivalent"\? If OEM that would be very disturbing!
Ken

The points came from Motobins, UK.
They state: "POINTS SET-ALL TWINS 1970-1978. 100% GERMAN MADE."
So I guess they are an aftermarket "equivalent".

Here they are:


The short occured on the terminal where the black wire attaches to the points. The lug sits a little proud of the main body/frame of the points and had to be bent over (approx 60-80 degrees, I suppose). It bent out of the way very easily.