Boxerworks.com

Hi all,

I've got a '78 R80/7 that I recently replaced the battery in. Upon installing the new battery (a Duralast with 400cca) the bike fired right up as usual but died after about a minute of idling. Since then I have no spark to either plug. I've checked the points and they're opening and closing fine. Any hints on what to check next? I've read up that the condensor may be bad but that's pretty rare. I have a feeling that its something pretty straight forward but its got me scratching my head.

Thanks for any advice.

Brian

Check all your battery connections. Seems unusual that something else has failed. Check back on the most recent work.

Kurt in S.A.

You might start here. http://w6rec.com/duane/bmw/points/

Thanks, Dbl checked the battery connections and all is good there as I'm still getting power to the instruments and the starter. I'll give Duane's article a look and start sorting through it.

Check for voltage at the points.
If you don't have 12 volts there, with the key-switch ON, you have some wiring to trace.
Back in a little while!! Gotta find the schematic.

No spark at all suggests on power to the coils OR a totally shorted capacitor OR capacitor lead. It's not unheard of for the long wire to the capacitor to be pinched and finally short to ground.
On these bikes, GREEN wires are normally HOT with the switch ON...BROWN wires or combinations of BROWN and a stripe are GROUNDED eventually.
The power for the coils goes from the battery to the ignition switch and leaves the switch on a green wire to the fuse panel. Fron this SAME side of the fuse panel (coils are not in fused circuit) power goes thru the emergency STOP switch and then to the coil primary terminals.

Take the tank off if you haven't already done this and start at the coils' primary terminals, with the switch ON, and check for 12 volts.

Thanks Jean, I'll head out to the garage at lunch today and start tracing.

Check in later if you get "lost" and I'll try to lead you thru it...I hope no one has messed with the wires inside the headlight shell, etc. Colors I mentioned are OEM colors!

So there's power going through the headlight and to the coil. I've got 12v at the green wire on the left hand coil. Are these powered in succession in that the left is powered first? The lower terminals of the coil where the jump from left to right is are both at 5.3v. There's only a 0.13v reading on the right side top terminal though.

Yes, the coils are in series so technically the left gets power first then the second...though you wouldn't really seen any significant time differences. Make sure that jumper wire between coils is crimped solidly and/or not corroded. If not, you could have a serious voltage drop right there.

Kurt in S.A.