Vintage BMW Motorcycle Owners

This '85 R80 RT has been rock solid...until now. It had fresh gas in the fall, and stabilizer in the fuel all winter. It fired right up after I put a new battery in it, as it always does every year. I drove for about a mile, and it died, acting like it ran out of fuel. I let it sit an hour, and it started again, but only ran for a mile or so. Now it won't start. I've pulled a fuel line off to make sure there was no blockage. Fuel came out just fine. I checked the plugs, and they weren't fouled. I checked that the plugs were getting spark. No problem. I'm looking for recommendations on what I should look at next.

First thing I would check is pull the float bowls off and look for water in the gas, despite fresh gas and stabilizer, you still may have it. (I filled up the other day at a station and ten miles down the road my bike started running on one cylinder, the gas station gave me a nice mix of water and gas at the pump. I had to drain a couple of gallons out in order to sort things.)

Oh, I am not sure how you checked for spark but on the 85 bikes, you MUST be certain the spark plugs are well and truly grounded. Failure to do so, could damage the ignition module in the electronic system. Not saying that is the problem now, just a caution.

Not knowing the condition or maintenance record of your bike, I would also suggest checking the valve clearance first, ignition timing second and finally is your choke system working as it should? Good luck. St.

Any luck? St.

Greg:

I had a similar problem with my R90/6. I thought it was gas and put it on reserve. But it turned out to be electrical. I narrowed it down to either the "light relay" (put in that model for police lights and siren) or the ignition switch. I replaced both and now it runs fine.

Craig

Thanks for the ideas, folks.

The old gas was slightly "yellow" when looking in the carb bowls. I drained all the old stuff out, and put in fresh, "clear" looking gas. It felt like it wanted to start, but no dice. I did notice, however, that after cranking for a bit, I accidently hit the kill switch, and it backfired big time! I replicated that a few times, so I'm starting to suspect electrical problems. As someone mentioned, that's what it turned out to be the problem for them.
I previously mentioned that I saw good spark when cranking, and yes, I grounded the plugs well when testing that.

So how do I continue to troubleshoot electrical problems?

Since you have one of the later ignition systems with a Hall effect sensor, I wonder if you might have an issue with. When you mentioned the kill switch toggle caused a spark, that pointed me to Snowbum's site. This is a lengthy article, but he mentions the issue with sparking when the kill switch is used:

https://bmwmotorcycletech.info/Ignition.htm

A simple thing to try is spray some contact cleaner into the kill switch and see what happens.

I suggest before you start any trouble shooting you get yourself a good wiring diagram. The best I have found are from EME they are in full color, and have pin locations numbered as well.

So if the cleaner doesn't work, try bypassing the kill switch. From my experience the Hall effect and ignition modules get blamed for a lot of stuff when it is not their fault. Yes, they have been known to fail but failures from what I have experienced in my own bike and in others I know, are VERY rare. You said the bike ran fine when stored, I would find it hard to believe the Hall effect would quit working while the bike was sitting. So what could happen when the bike is sitting? Corrosion, moisture? Try the simple things first.

I give my long time example of having a misfire on my bike which I thought was due to the Hall effect and other ignition components. Long story short, I replaced or swapped parts out right and left only to finally find the problem was due to a dirty ground. LOL, lucky for me I had no cost involved as I have a selection of good used parts on hand but if I hadn't, it would have been an expensive episode.

If you are near Rochester NY, I could stop by and lend a hand if interested? St.

Greg:
The problem I had was difficult to trace because It would work when things cooled down. By the time I got the headlight apart and could check things with the meter, everything had cooled down and was working. I had to run it with the headlight apart for half an hour before it failed. St is right. Check all the ground connections first and spray the contacts with cleaner. On a breaker point system I would say change the condenser. Also double check the timing.

Craig

I had a similar problem. It turned out to be the coil (s). They short out when they get hot. And fix themselves when they cool off

Thanks for everyone's help. I cleaned as many contact points as I could find. No dice.
I decided to chance it was the ignition module. I ordered a replacement, took the gas tank off, removed all the sticky-but-mostly-dried thermal goop from the heat sink. I replaced the ignition module, using the supplied thermal paste, and put it all back together.
It fired right up, and is purring like a kitten again. (I can't understand how I was getting any spark with a dead/dying ignition module, but I guess it'll still spark, but not within correct limits? Dunno.)
Anyway, I'm back on the road again.
The OEM part was: BOSCH 0 227 100103
New part: Enduralast IgnMod-R284