Fuel delivery verses ignition failure.

[SteveD]

Edit: fuel issue, not HES.
1981 R100RS.
On the freeway on the way to work was first. Bike died, coasted to a stop on the side. Initially I thought it was slow to catch when hitting reserve, but it's usually ok when that happens. It would crank over but not start. No needle movement at the tacho.
Fuel in the filters looked unusually "globulously" dirty, so I flushed the junk out, let a bit run onto the road from the carbs. The bowl had a large brown watery glob in it to. After about 15 minutes, it started up, and I proceeded to work thinking I'd done good!

Coming home, about the same distance, it did it again. This time it started up after 2 minutes, but only made it another 3 kms before the third time for the day. 3 kms from home.

Had a another look at fuel. Bowl somewhat watery in the other carb, but not as much. Same procedure. No fire.

Headers equally warm, plugs gray/white, look good. Tank off, fiddle with the coil HT wire connections. Bike starts up. This was about 15 minutes later, so a similar cool down time to the first episode.

Fuel or something heating up/cooling down?

I've done two things lately.
1. Synced cables. Runs better (when it does run) two days ago.
2. Changed the parking light bulb, which has been blown for ages. It still works. Done yesterday.

All the idiot lights work as they should. All lights, etc work as expected. VM shows usual charge, battery appeared to crank over ok, but without starting.

Car to work tomorrow, then after work drain the tank and flush it. That has been done a few months back.

THOUGHTS? Hopefully some bad fuel.

[enigmaT120]

Was it a new tank of gas? Where did you buy it? Parked or ridden in the rain lately? I've never had bad gas, except from Dennison's chili. And I just live with that.

A guy on the Brit-Iron email list says he knows of 4 British motorcycles around the web that have all started having the same symptom. Unlike him I do believe in coincidence, especially if I'm primed by my own experience to see them, but I'm tempted to tell him German bikes are catching the new world wide motorcycle plague.

[Bamboo812]

Gunk in the bowl killing an engine means more further up. I'd clean the carbs, but at the very least drop the idle jets and main jet holders and clean them. A tiny piece can plug the idle jet, but an amazing amount of sludge can be sucked up through the main and become trapped in the area around the needle jet. Note: while easy to remove jets while the carbs are on the bike, replacing them is best done on the bench...

[Major Softie]

Regardless of the icky stuff in your fuel, next time it happens immediately pull a plug and check for spark. I'll bet you don't have any. Both ignition triggers and coils can fail when they get hot.

If it was the fuel, there's no way you would have both cylinders instantly die together, but it's still a good thing you got that crap out of there.

[Duane Ausherman]

MS +1

[SteveD]

Thanks all. The other thing I haven't tried is opening the feul cap to check the venting. The coil is only a few months old, a dyna blue being used with late issue ICU. I did remove the tank and ensure the ht leads were at least correctly seated and the earth wasn't loose.
First thing will be to clean the tank and check the vent as they're quick and easy.

[ME 109]

Check your key ignition Steve, grab the wires and move them around, and wiggle the key to see if there is a bad connection.

[SteveD]

Good idea Jeff. I was jiggling the parker wiring when replacing the blown bulb ....maybe i've disturbed something doing that.

[Bamboo812]

Another thought; a friend here on the island had intermittent missing that was getting worse. Bike was dying at stop signs and idling very erratically. When checking the timing with a strobe, the light would go out when the miss was happening. Everything pointed to a failed Hall sensor, but it turned out to be bad connection at the kill switch. Pulling the switch off and spraying contact cleaner fixed the problem completely.

[ME 109]

......... but it turned out to be bad connection at the kill switch. Pulling the switch off and spraying contact cleaner fixed the problem completely.

There'd be no power to the starter or lights with kill switch on/defective.