Cafe'd R100 - Ignition problems

[Guigsy]

Hi,

A biker mate (who isn't into internet forums) has spent most of last year with spanner help of a local mechanic turning an R100RS into a cafe racer... No, it's not a GS, but I'm hoping you guys will be able to help with your airhead knowledge!

The bike usually starts fine and runs nicely, but has an intermittent issue, it randomly cuts out and refuses to come back to life for a period of minutes. When it's playing up, the starter motor merrily turns over, but it never even starts to bite. Leave it a couple of minutes and it'll fire up before you can blink. Before we've managed to get all the way from Birmingham to Stratford on one occasion, other times we have an issue within a mile. Sometimes it just stutters for a short while then continues on, but most of the time it just stops dead.

It has new coils, a new battery and the battery always seems to be strong. Most of the old wiring loom has been replaced to squeeze it all under the tank.

First piece of useful diagnosis: when it stutters, the gen light flickers. When it cuts out completely, the indicators, brake lights and headlight still work.... but there's no neutral/oil/gen light. You know that when the dash comes back to life, it'll restart. We're guessing it's something in the ignition circuit, but the mechanic is clueless with electrics.

Picture... overt your eyes if you don't like retro modernisations:

Another probably unrelated piece of information... It's also had an electrical fire in the loom running up to the (Yamaha) kill switch. The mechanic bypassed the switch and that bit of the loom has been replaced. It's not happened since... but may be another symptom of the same issue?

If anyone has any ideas what it might be or any suggestions for further diagnosis, it'd be appreciated.

Thanks,


Guigsy

 

[PaulRS]

Nice bike.

I'd check and check again the kill-switch and associated wiring.

Because what you see is exactly what happens when I hit the kill-switch on a R100RT standing here.
That switch cuts out ignition and the oil-gen-neutral lights on the dash, indicator and Hi beam lights on the dash still works, as do all the lighting, starter motor and brake lights.

Paul.

 

[Kenny]

As above re kill switch. Very hard to diagnose as bike is obviously non standard. Best to switch on the ignition and gently pull wiring ( used to be a more common fault of the wiring being trapped near the frame/forks top and breaking the odd wire to the clocks/ignition ) to see if there is a breakage in the wiring.

 

[Guigsy]

I'll pass it on, thanks guys. Although most of the wiring is replaced, it still has it's original clocks (at the moment) along with the ICU, bean can, rectifier, alternator, etc. Here's another pic:

Is there anything we can check to eliminate other possibilities?

 

[Wrigsby1]

Much as I dislike the hackneyed cafe racer/bobber/project crap that gets put around the net, I think that is a great looking bike... Nice one...

You can also have random cutting out issues with the ignition switch contacts being corroded... I am not sure if the airhead switches are the rebuild able types but if they are check the contacts at the bottom to rule that out... Also does the dash come back to life at a set time after the cut outs or is it random...? Is the bike always hot when it happens?

 

[Kenny]

OE clocks...just check the harness screws up tight ( and clean ) into the unit ( you probably have but never know )

Oh and agree with above, lot of nice work gone into that bike

 

[Guigsy]

The annoying thing about the issue is that it's fine for a while, then (most of the time) it either stutters for a few seconds before dying, or it just completely stops firing dead. It'll then refuse to start for a couple of minutes (with missing lights on the dash). Leave it alone (no jiggling) and next time you check, the dash will come back up, it'll start immediately on the button and run fine for at least a minute and possibly for an hour...

 

[Rob Farmer]

Sounds like a crap wiring harness. Did he butcher it himself or pay somebody else to do it for him?

 

[Guigsy]

He paid someone to rewire it all. At first it had quite a bit of the original BMW loom spliced into the switchgear from the Yamaha front end. Pretty much all of it has been replaced now.

It's annoying that the rest of the bike has come together so well. When it runs, it's smooth and it sounds really good. Just it cuts out...

Spoke the my mate (the owner) this morning. Last night he had a play with the ignition barrel. It's slightly corroded, but wiggling the connections around didn't make it cut out. As the ignition is cheap (and it looks like it might be for a car rather than a bike) he's going to replace it anyway to try and eliminate potential problems. I'm heading over at the weekend. I'll try to follow the ignition back through the loom to see if it's got a dodgy connection somewhere along the line.... no, I don't know what I'm doing either.