Hi all, a little bit of help needed please. Low speed cylinders cutting out on my '85 k100 (naked with an RS fairing). Checked the past topics, the culprit seemed to be the coil as the problem is the engine would only run on two cylinders and the tacho would stop working, then the two cylinders would fire up, as would the tacho. Checked the coils, they were the older, original type still. Bought some newer type as the topic suggested with the orange bits on them, fitted them yesterday, cutting out problem persists. My commute to work is about 5 minutes of town speed, 20 minutes at 100kph speed, so the twin cylinder problem is not a problem for long and once at speed, the bike runs well. Other work to the bike includes, new plugs, ignition switch taken apart and cleaned (looked brand new still) and EME plug leads were fitted last year. This problem has only started about three weeks ago.
Any other suggestions to sort out the problem would be most appreciated. Many thanks, Dave.

A bit confused. Is it running ok then cuts out or is just not starting nor running on 2.
"Cutting out" implies its going ok then stops.

Try these

• Check your spade connectors on the bottom of the coils particularly the earth connections.
  
• Make sure the ICU plug is clean and properly seated. This is a common problem.
  
• Make sure the HES connector plug front/right under the tank is clean and properly seated.
  
• One of your HES may be Kaput.
  

Hi Holister, thanks for the reply. I'll try to be a little clearer. Bike starts and idles fine, as soon as I pull away it intermittently runs on two cylinders and the tacho stops working. Once out onto the open road, it's fine. When I get to the town where I work, it will often drop two cylinders and the tacho stops working again. As mentioned, I replaced the original coils a couple of days ago with a pair of the orange tower coils to try and fix the problem, but the problem persists. So, the issue happens hot or cold. Any more thoughts from anyone? Cheers, Dave.

Have you any way of determining which two cylinders are causing the trouble? The tacho signal comes from one of the coils and both coils get their signal starting from the Hall Effect Sensor.

If one of the sensors is acting up it will interfere with the signal for either 1&4 or 2&3 and will affect two rather than one cylinder.

I cant remember if its 2/3 coil has the tacho signal but its pointing to one of the sensors or to damage to the wire from the HES to the ICU.

Check and clean plug and pins on ICU. Can you swap the HES with another?

Still points to Holister's post.

FYI: There's two black/blue wires from the 1&4 coil. One goes to the tach and the other comes from the ICU.

If the tach goes out when you're running on 2 cylinders then I'd guess it's the 1&4 coil not firing.

One of the following may be the culprit:
1 - ICU going bad or connector loose
2 - One of the HES sensors or its wiring going bad.

The HES wiring is zip-tied to the right frame member that goes to the engine.  You can try wiggling that to see if the HES wiring might be the issue.

If your 2-3 goes out the engine stops because the ECU gets it's signal to fire the injectors from that so the 1-4 coil/HES is where I would be looking for starters.

Many thanks Olaf, Rick and Duck for the excellent info'. Gives me something to work with and I've got plenty of spares, so we'll see how we go. Thanks again, Dave.