I have almost finished the total rebuild of my 1987 CBR1000F but when trying to start, it doesn't. The spark is very weak, but I note that the horn and headlight only work when the clutch is pulled in! The battery is fully charged. I am assuming a short circuit, but where? Any ideas gratefully received

Leofwen

 

Seems like a bad ground to me. From what I could see from a wiring diagram I found the only common nominator between all is the left side handlebar switch box or whatever it's called. Seems like the horn and the headlight dimmer switch might be grounding out through the clutch switch. Deffy worth a peek, the contacts do tend to oxidize over the years causing all kinds of funny and weird stuff.

Just be careful with the switch if you open it, there are small bits and springs under tension ready to fly into the oblivion at the first chance so if you can better dismantle the switch gear in a plastic box or the likes to catch any flyers. At least keep your hand over it or chuck it into a clear plastic bag or something, looking for a lost contact slider on all fours under the garage tables is not a fun task...

 

Thanks for that Matson, I do suspect a bad earth, especially as I have had the frame powder coated. I'll strip the switch and post my findings.
Incidentally, where did you fond a circuit for the 1987 F? I can only find one for the H onwards, which of course adds to the difficulty I have had in tracing the fault.
Regards
Leofwen

 

Honestly I didn't even check what year it is for, switchgear wiring is pretty much the same in all cbr:s, I was basically just checking a theory if a shorting wire inside the casing could cause that and in my opinion it looked plausible. Powdercoating the frame definitely means checking you have good ground on bare metal everywhere where it's needed, not fun chasing your tail because a loop connector is carrying on the paint edge somewhere creating an intermittent contact.

 

Thanks Mattson, I think we are on the same wavelength on this. I'm sure I will eventually find a bad earth. The original problem of a weak spark seems to be caused by poor HT leads with too high a resistance, I am replacing the leads and hopefully AOK!
Thanks for your help. Fantastic to be part of a worldwide group with an interest in the CBR.

Regards
Leofwen

 

Just to be sure you know, if you're making your own leads and not using OEM replacements, make sure you are using copper core wire, having too much resistance hints someone had made the current leads themselves from the carbon core stuff they use in cars, which is not suitable for motorcycle use and worst case scenario migh fry your coils.

 

Yep I am. I was aware of that. The high resistance was caused by corrosion. Before the rebuild the bike had been stood in a wet barn for ten years. But once again thanks, you could have stopped me from making an expensive mistake.