Boxerworks.com

Hello everyone, first post here.

I've owned my first airhead for a month now, it's a 1985 R80 Monolever. Really nice bike and already've got my hands dirty a number of times

A week ago it misfired a few times while driving, it was a warm day and the tacho needle went to zero when the problem occurred. Finally wouldn't run anymore, would start but die instantly. After some measuring thought it was the coil as the primary had a 4,7 ohm resistance. Replaced that with 3,0 ohm Harley unit, didn't help. Found a bad contact at the ICU connector, fixed that but no help. After more measuring I came to a conclusion it must be the ICU.

So, with the original Bosch 0 227 100 103 ICU it will start, but dies instantly. I've bought three ICU's so far, with the first one it wouldn't start at all, with the other two it will start, but the timing is retarded so much I cant get it adjusted and the bike wont rev more than 1500. Struggling to idle too.

Where can I find a working ICU? 153€ at the BMW dealer...

Could it be a problem with the bean can? I replaced the advance springs in that, that solved the high idle issue. The hall sensor tests fine, triggers twice per revolution with around 90 degree zone where it is switched on. I could drill a new pin hole and rotate the cog on the ATU, but that doesn't sound too tempting.

Welcome! As I recall, these ICU or modules need to have the heat sink paste renewed periodically. This helps draw heat out of the module. Be sure you do that.

Kurt in S.A.

Yep, found no paste on the original, that’s probably why it died.

Also, tight valves can contribute to poor idle. Make sure they are set at 0.15mm intake and 0.20mm exhaust.

Kurt in S.A.

I actually checked and adjusted the valves after the second module wouldn’t work, no change on behavior.

I have seen more than one instance where freaky ignition/ICU issues were traced down to faulty tachometers.
Try it with the tachometer disconnected and see what happens.

I’ll be damned, that solved it! Still have to check if the new modules retard the timing, but now it runs and responses to throttle.

You're welcome.
It's the simple but often overlooked and undocumented solution to problems like yours that compelled me to come back to the forum.
The bad news? A tach probly costs a lot more than a ECU.

Well I still need a new ICU, timing is still too retarded (can get it to OT, but not any further) and the original seems to be toast. Thank you!

The timing advance/retard is done by centrifugal the weights in the beancan.
Rotate the beancan so you get the "F" mark at 3-4000 rpm and see what happens when you let it drop back to idle.