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Topic-icon 80/RT Intermittent spark, what do I look for

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3 weeks 9 hours ago #4731 by 82
1983 80 RT, bike will start and run then just quit, crank it over and will not start and has no spark, if I flip the kill switch back and forth it will cause a spark and ignite the fuel air mixture and cause anything from a slight puff to a full backfire. It will then start, sometimes it will run for a few seconds sometimes a few minutes and sometimes for a good long time. I have replaced plugs, wires, ecu, cleaned connections at the kill switch, and under the tank. I know intermittent problems are the hardest to diagnose. the only thing I have not replaced is the bean can, could this be it?? It used to only do this very occasionally and was not an issue, bike has now been stored and the problem is much worse than before. any ideas would be helpful.

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3 weeks 5 hours ago - 3 weeks 4 hours ago #4735 by Wobbly

82 wrote: It used to only do this very occasionally and was not an issue, bike has now been stored and the problem is much worse than before. Any ideas would be helpful.

Welcome Aboard !

• If the fuel in your bike is over 8 weeks old, get rid of ALL of it. Yes, that correct... tank, fuel lines, and carbs.

• If you left fuel in the bike while it was in storage, then the carbs are going to need the float bowls popped off and examined for varnish and scum. If you see any thing except sparkling clean float bowls, then the jets and needles will need removal and cleaning, or complete replacement.

There's a good section on carb cleaning here... www.airheads.org/forum/technical-discuss...ead-back-on-the-road

► Trying to start the bike with old fuel will permanently foul the plugs. After you install new high test fuel and clean the carbs, then you can install a second new set of NGK BP7ES plugs and try again.

82 wrote: I have replaced plugs, wires, ecu, cleaned connections at the kill switch, and under the tank.

And did you renew the heat sink compound when you installed the new ECU ?

82 wrote: It used to only do this very occasionally and was not an issue...

With no malice intended, but trying to correct the thinking to prevent future repeats....
The root cause is most likely stale fuel. It was always an issue, but one that got ignored until it upgraded itself to full fledged problem. Now instead of $10 worth of fuel system cleaner and a nice long Spring ride, this bike is probably in for $100 in parts and 4 hours of labor. This is why we repeatedly advise people to empty all the fuel if you're not going to ride at least once a month.

Hope this helps.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 3 weeks 4 hours ago by Wobbly.

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3 weeks 5 hours ago #4738 by 82
fuel had been drained and is fresh, no carb issues, when it runs it runs great thru all rpms. It will just cut out with no spark.

yes I put heat sink compound under the ECU.

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3 weeks 4 hours ago - 3 weeks 3 hours ago #4744 by Wobbly
Excuse me for my insistence on fuel issues, but they constitute about 95% of the problems shops see... especially when the word "storage" gets mentioned.

There is one other problem area for you to check. It shows up more commonly on the bikes with the under-fuel-tank brake master cylinder because the leaking brake fluid is usually the root cause. I have a 1983 R100 in my shop right now and I checked this out. The power for EVERYTHING on the bike is routed through the starter relay, which is a 1x1x1" plug-in "mini-cube" type relay. ALL the bike's power enters on one #87 lug, and exits on another identical #87 lug. (Thus the name "Dual 87 Relay".)

If there is any corrosion on EITHER #87 lug, then the whole bike (ignition, lights, blinkers, etc) will go intermittent. You only witness the ignition stopping, but I'll bet everything stops.

STEP 1 - I highly suggest you remove your fuel tank and locate the lone relay on the LH side of the frame. Pull it straight up and out of the relay socket. If you see any corrosion on the pins, then replace the relay.

Typical "mini-cube" relay

STEP 2 - Stick an ice pic or dental pick into the socket and gingerly tighten up the contact force on the socket contacts.

STEP 3 - Treat each of the male prongs on the relay with a coating of No-Ox-Id conductive electrical paste before re-inserting the relay into the socket.

Photo No-Ox-Id available on Amazon

STEP 4 - In fact to double your chances of success, unplug the ECU which is atop the brake line junction just inches away. Carefully coat each of the tiny electrical contacts on that large connector too. This will improve the electrical connections AND exclude water from the ECU connector.

Hope this helps.


Hella "Dual 87 Relay" on Amazon

PS. I still think you could benefit from running StarTron fuel treatment for a month. :P

Don't hide 'em, Ride 'em !!
#15150
Last edit: 3 weeks 3 hours ago by Wobbly.

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3 weeks 3 hours ago #4746 by 82
I have cleaned all the terminals on the starter relay, when the engine quits nothing else seems to be effected, lights etc all work and there is no dimming, just the ignition cutting out and the bike quitting. got in a bit of a ride yesterday and it ran ok. this morning it started ran a minute or so and then quit. then would not fire at all. could still get the pop if I toggled the kill switch after cranking it over, but would not start.

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3 weeks 3 hours ago - 3 weeks 3 hours ago #4752 by Wobbly
Sorry, that's my best shot.

Consider 40 years of water being thrown up on every electrical connector. I'd be treating every contact within every connector that has anything to do with ignition with No-Ox-Id.

All the best.

Don't hide 'em, Ride 'em !!
#15150
Last edit: 3 weeks 3 hours ago by Wobbly.

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