Just barely got me home

[Mrducati]

I just barely got home on my newly bought '89 R100RT tonight. It stopped for a second - worked - stopped and worked very eratic. It felt like a carburetor/fuel issue, but I am puzzled because it has two carburetor. If one carburator was clogged, the other cylinder should produce some power! It came to full engine braking each time it stopped. I did rev it up a few times to see if I could draw throu any debri from a carb. And eventually stopped and gave the carbs a few knocks with a spanner to see if I could get something unstuck. It did run fine the rest of my trip, but I didn't feel very confident. Any thoughts on this? Fuel or ignition? This is a 89, so it should have the electronic ignition. Is there any common problems with these that could explain today's hiccup?

[Kurt in S.A.]

One issue, though it's usually persistent, is the heat sink paste that doesn't transfer heat from the ignition control module. It needs to be renewed regularly. If the heat is not drawn off, the module overheats and shuts down.

On the fuel side, could be that the tank is building a vacuum if it doesn't vent, thus starving the carbs. A way to check that is, when it happens again, safely reach down and loosen the gas cap. If it improves in a few seconds, that's the issue.

Kurt in S.A.

[SteveD]

Systematic assessment required here.

Easiest first.

Float bowls off. Main jet off. Check for blockages.

Check the fuel flow. It should run freely. Remove any external filter after the first test to see if they had a blockage effect. If you have the same problem riding it again, stop immediately and turn the fuel off. That stops any further flow so you can assess if the bowls are full or not. If full, it's not a fuel flow problem. If the bowls are less than full, remove the taps and clean their internal filters. I've had this happen to me..both blocked.

Whacking the carb might've worked. There have been reports of the floats sticking to the bowls. Your intervention is the prescribed one. Maybe a slight squeeze of the floats together will sort that?

No venting fuel cap..described above.

Tank off. Check two things.
1. The ICU heatsink paste. Two small fasteners off and inspect the paste. Clean the surface, reapply a smidge of new paste. It's likely never been replaced.
2. The coil. It should be a single dual coil. If it's oem BMW there was a problem with the grey coil, aka the Crack-o-matic...because it cracked and caused your symptoms. If the coil is black, is marked Made in Slovenia, and the outlets are red, then it's not a C-0-M. That's good. I'm unsure when the C-o-M was replaced as the oem coil.

If those two issues don't solve the problem then follow this:
Troubleshooting BMW-fitted electronic ignition Airheads 1981-1996

* Disconnect battery neg from battery before removal of the front engine cover.

Disconnect bean can 3-pin connector below diode board. It has a wire bail that is a PITA to remove.
Use a hooked pick to pull one end of the clip and the connector will release. Handle the connector carefully, old ones often crumble in your hands. If that starts to happen, MARK each of the three wires as to position, and make a note of the marks. You can insulate the three wires and connect them individually as a makeshift.

Position a wire or straightened, unpainted paper clip into the centre female terminal on the harness side of the connection.

Remove ONE spark plug. Reconnect the plug to the HT cable, firmly ground the spark plug in a location where it cannot fall off, has good ground and where you can clearly see the spark. Best in low light.

Reconnect battery, turn on IGN switch, kill switch ON. Instrument lamps ON.

COIL and WIRING TEST: Flick kill switch on and off as you watch the spark plug. Got ONE spark each time? The coils are OK, stop suspecting them.

BEAN CAN TEST: Scratch the paper clip across the alternator housing (unpainted aluminium=good ground) like striking a match, while looking at the spark plug:

IF you see spark as you scratch the paper clip across ground, the BEAN CAN is bad - probably failed HES. Repair or replace bean can. BMW doesn't sell them anymore.

If you DO NOT SEE spark, most likely culprit is the Ignition Control Unit under the tank. (By process of elimination.)

If you remove or replace the ICU, clean off the mount, remove and replace the old heat sink compound. Don’t install without heat sink compound. Replace it every few years. More if you ride a lot in hot conditions.

• Don’t forget to disconnect the battery before reinstalling the front cover.

Paraphrased from a Tom Cutter article.

edit: one more thing. Sometimes the ignition switch can play up. Do you use a heavy set of keys? If so, stop it!

[tsa]

I just barely got home on my newly bought '89 R100RT tonight. It stopped for a second - worked - stopped and worked very eratic. It felt like a carburetor/fuel issue, but I am puzzled . . . Fuel or ignition?

Good advice given on the Ignition Unit heat sink paste, and the "Crack-O-Matic" dual output coil these bikes had as new.

I wonder if the monoshock boxers are wired in the same was as earlier twins? When I had a 12V supply lead going to an aftermarket electronic unit break, with immediate cutting out of the engine, it could be seen by the tachometer needle instantly dropping down to 0 revs, since my rev-counter picks up its signal from one of the coils. Thus I had the "ignition or fuel?" question answered while I still was coasting to a stop at the side of the road.

You mentioned you had a minor fuel leak. Is this also the case when parked overnight with the fuel taps turned off? If stood for a long time with condensation inside the tank, minor rust holes can develop (a). I think it is more likely that your leak is due to (b) perished rubber fuel hoses, or ditto float valve not closing properly. First you need to sort out if a) or b) is the cause of your leak.

[Chuey]

Symptoms similar to what you describe happened to me. It turned out to be a ground problem. Under the tank, the coil(s) are held in place by four 6X1mm bolts. I think it is the front left one that was loosened. There are some brown wires that go under that screw, or, it could probably be any of the four. That connection is very important. It is so easy to check that you may as well, and I made sure there was good grounding contact before retightening.

Chuey

[SteveD]

Always wise to check the simple stuff first. Grounds at the battery neg and the coil/main frame just about the first thing to check. The coil on the mono is different to the TS and in a different spot, so the earth will likely be different too.

[Beemerboff]

The connections on the solenoid can slacken too, and on some bikes the auxiliary power is picked up from the live side.

[Mrducati]

Thank you all for thorough advice! I really appreciate that! Troubleshooting is always a challenge when the problem isn't constant. Now I have several areas to check!

[Wobbly]

Another perennial favorite is the disintegration of the ivory 3-ping connector coming out of the ignition hall sensor can under the front cover of the engine. When that plastic connector crumbles, the ignition goes intermittent. Rick Jones (Motorad Eletrik) sells a new connector that quickly fixes the issue. The harness side of the connector is fine, it's always the ivory-colored sensor side.

[Mrducati]

I've found the petcock to be almost blocked. I've ordered a new one. And the carbs are cleaned up (and leaking fuelbowl gasket replaced), the fuel-lines are renewed, and I've new heat-sink paste on the ICU and cleand up electical Connections lots of Places, the tank is venting just fine, and observed that my coils are black an made in Slovenia.
I feel this petcock must be the reason for the trouble I've had lately. Just have to wait for it to arrive first.