Intermittent ignition fault

[ChasF]

Set off this morning to ride back home. 5 miles up the road the ignition just cut. I pulled over and tried to start the bike, it was firing but wouldn't run. I flicked the kill switch a few times and this resulted in a loud bang in the exhaust. The bike started immediately and we carried on. It cut out a couple more times but picked up again after a few seconds, then passing some cars up a steep hill it cut out so whilst still rolling I flicked the kill switch resulting in the loud explosion in the exhaust ( must have frightened the shit out of the car driver) and we carried on. It probably cut about 20 times over the next 150 miles but we only had to actually pull over twice. About 5 miles from home we couldn't seem to get it going for more than about 100 yards at a time but eventually got back.

I've just changed the kill swtch/starter button as I had a new one here and also fitted the secondhand amplifier that I've been carrying around for the past 25 years but never tested to see if it works. Bike seems to run fine but I'm just concerned that the intermittent nature of the fault might be an indication that the bean can is on it's way out.

Anyone had a similar fault?

 

[DrFarkoff]

Sounds like Hall sensor

 

[ChasF]

Had my suspicions, thanks.

 

[solidstate100]

I had similar symptoms a few weeks back. Like you I supected the hall sensor BUT it turned out that the back of the ignition switch (the plastic bit with all the connectors on it) was loose/coming away from the alloy body (decades of vibration no doubt) and intermittantly making/breaking contact - needed the crimps retightening with a pair of longnose pliers and all good.

 

[ChasF]

Thanks for that. Thing is when it cuts out it cuts completely - doesn't stutter or misfire although sometimes it comes back on with no intervention most times it seems to need the kill switch turned off then on to get it going again. I need to go on an extended ride to see if the changes I've made already have changed anything.

I need to get it fixed properly as we've got a couple of long trips coming up and the missus isn't keen on being left stranded. We were only discussing yesterday, at breakfast before we left, that the old girl is showing her age and perhaps we should get something more modern for the longer runs.

 

[Florence]

You need a 1200gs in yellow with that old airhead in part exchange

 

[DrFarkoff]

Chas Also its worth checking if the heat sink paste on the Inition amplifier has dried up

I'd definitely be sticking a replacement amp on there and going for a ride Before chopping out hall sensors etc

Thanks for that. Thing is when it cuts out it cuts completely - doesn't stutter or misfire although sometimes it comes back on with no intervention most times it seems to need the kill switch turned off then on to get it going again. I need to go on an extended ride to see if the changes I've made already have changed anything.

I need to get it fixed properly as we've got a couple of long trips coming up and the missus isn't keen on being left stranded. We were only discussing yesterday, at breakfast before we left, that the old girl is showing her age and perhaps we should get something more modern for the longer runs.

 

[ChasF]

Thanks, yes the paste had dried up. I cleaned both faces with wire wool and put a smear of heat sink compound on the 'new' amp.
Strangely enough, the new amp which is a Bosch that I bought secondhand from James Sherlock back in 1990 and it's been in the tooltray ever since, seems to work better than the Telefunken one it has replaced - certainly the bike start much more easily.

 

[ChasF]

Looks like it was the ICU. A few more test miles required before I'm absolutely sure.

 

[B Murr]

Looks like it was the ICU. A few more test miles required before I'm absolutely sure.

Excuse my ignorance, but what is an ICU when it's not intensive care unit?

 

[ChasF]

Ignition Control Unit - another name for the ignition amplifier

 

[ChasF]

After doing some miles in the last few days with no recurrence of the fault it would seem that it was definitely the amplifier. As DrF says a good thermal contact between the amp and heatsink is important but failure was probably aggrevated in my because I have the bad habit of only turning the engine off at the kill switch.

I've renewed the heat sink compound on my R80 as well.