Sudden engine stop on MK III

Hello and happy new year to everyone. After having restored my Interstate 850 MKIII last year I had some nice autumn-rides here in germany. The machine was performing well but lately I have encountered the following problem: after kick-starting the motor (1 to 5 kicks) it runs well on the choke and also after the warming up without choke (Mikuni). But then, suddenly and without any bad-running or incidence, the engine stops, and it is impossible to start it again. When I take the plug out there is only a very weak spark to be seen. A day later, the engine would start again, but only for the same short time.

Does anyone of you have an idea what the reason for this behaviour could be. My guess is an electrical problem, but I do not know how to approach it. Looking forward to your comments and thanks in advance.

Thomas

Left out type of ignition here's some things about universal to check, ugh, again and again for too many of us.

1. Bad connection hidden inside insulation, usually trigger lead under cover.
2. Bad ground to ignition.
3. Bad power supply through key and-or kill button - battery terminal - fuse.
4. Coil gone south, usually fails with warming or vibing.
5. Bad connection way away from ignition and engine, like tail light ground strap slapping the power side in random bumps and times.
6. Expect plugs to get fouled after these shut downs so not bad ideal to try new ones, if not solved by above fault fixings.
7. Have a look at night while probing and tugging.

hobot said:

Left out type of ignition here's some things about universal to check, ugh, again and again for too many of us.

1. Bad connection hidden inside insulation, usually trigger lead under cover.
2. Bad ground to ignition.
3. Bad power supply through key and-or kill button - battery terminal - fuse.
4. Coil gone south, usually fails with warming or vibing.
5. Bad connection way away from ignition and engine, like tail light ground strap slapping the power side in random bumps and times.
6. Expect plugs to get fouled after these shut downs so not bad ideal to try new ones, if not solved by above fault fixings.
7. Have a look at night while probing and tugging.

Click to expand...

Thank you for those hints! Hopefully, I do not have to go through all of them - I think # 3 is interesting. I'll keep you informed about any findings.

Thomas

Maybe Coils or Condensor shot , If theyre original , theyre past there use by date .

If coils stinking hot when it cuts , its the coils .Should be touchable sans burns .

If Coil / points Ign. a ' hot wire ' battery to coil , leaves just the Points - coil wire
.IF it still does it then , its ( probably :lol: ) NOT the rest of the arrangement .

MANY Lucas keyswitches have been found to be at fault.

Are you charging the battery between these events? If so, you might just be running off the battery until it doesn't have enough power left for the ignition.

Russ

I had a similar problem. Mine was the kill switch. A crude system at best, if you haven't opened it up and cleaned it you need to.
JD75

I hadn't used my bike for several months, and it sat in my shed. Usually if I put fuel in it and charge the battery, it always fires up immediately. On the last occasion, it coughed once and refused to fire up after that. Seems the plugs can act a bit strangely of they have a bit of carbon on them, and are left sitting and then encounter fuel. I changed the plugs and it responded instantly.

Thomas, what is the ignition type?

My rough riding buddy Wesley has a small spring attached to his key because the bouncing and wind flutter has destroyed his switch connections prior to protecting it longer term. Ms Peel once had 6 things at fault 1000 miles away at a rally and each one gave exactly the same symptoms so had to ignore symptoms and just investigate each and every component which still did not solve the instant hi rpm rev up with LOUD back fires and headers turned bright red all the way to mufflers. Then I passed around a jar of 'shine which stopped our minds thinking so just observing to notice something amiss in the Boyer new trigger leads vibration to find last fault of trigger wire terminal nut behind magnets clipping them just enough. After much mis firing plugs can begin to foul up - as did in Peel case so even after all the above only ran on one jug, till a non R plug found for normal running but then turned Peel's LED signals into syncopated timing lights.

Commandos are a real thinking and drinking man's tester.

norton- racer, Did you ever find out what the problem was

Phil