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1980 CB750k Electrical Short Issues

bobaroski2121

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Hey Everyone,

Bought this bike about a year ago, been working on it every since. Bike was running well, aside from the things that affect an older bike but recently, I noticed that when starting the bike the starter would not always engage, but just spin. Sometimes it would work, sometimes it wouldnt. I decided to start self diagnosing the issue and decided to replace the starter solenoid. After ordering a new solenoid, I went to replace the old one and the 30AMP fuse blew immediately after plugging it in. I first reversed the cables from the starter hoping the M/B were mislabeled but didnt get power after doing so. I looked at the older solenoid and realized the previous owner wasnt using a standard 30AMP fuse, but a strip of metal he had soldered across the solenoid. I assumed this is why the starter was going bad. From there, I began tracing every wire through the bike to ensure there wasnt any short. I realized the previous owner had remove some components such as the clutch switch as well as some wiring harnesses as well. Using the factory wiring schematic I reran every wire to ensure they were connected correctly, aside from the two that carried current from the solenoid. I ran into one issue with the starter button as my after market starter only had two wires, and the diagram called for four, but for now I just connected two (as it was connected before, when it didnt have any issues). After doing that, I tried to reconnect the two wires from the starter that carry current, one to the clutch switch and the other to the starter switch. When connecting the wire that goes to the clutch switch, to the grounding wire (because the clutch switch has been removed), the fuse blows.

I then disconnected every component one by one until the fuse stopped blowing. I was left with nothing but the starter motor connected directly to the solenoid, nothing else was connected, once I removed the starter motor, fuse didnt blow.

SO, I assume its the starter motor and that it needs to be rebuilt. I just received a call from the guy who was rebuilding it and he says there was no short in the motor, and that it was grounded fine. He is rebuilding the grounding brushes and doing some clean up.

At this point, I dont know where else to check. I am picking it back up from him this afternoon and hoping the clean up he did might have fixed it and he just was misinformed.

If not, any suggestions on where to look next?

Thanks
 
Absolutely NONE of what you have messed with has anything to do with your original issue, all you have done is messed things up. The OEM fuse IS a flat strip of thin metal, not a normal fuse at all. You can unscrew it and patch in any kind of fuse holder you want there. Past that, I'm lost with what you have done after that, shouldn't be hard to fix that.

The starter spins free when the one way clutch does not lock. That has ZERO to do with electrical there, purely a mechanical thing. Often the 3 screws that hold the clutch together have come loose under left crank end cover.
 
Thanks, I had the starter motor rebuilt, and re did all the wiring and its no longer blowing the fuse. I couldnt identify anything specifically about the short, but the new solenoid I was using didnt use a flat fuse, just a standard 30AMP fuse.
 
Solenoid probably off a CBR600, common to swap those on there and many sell them saying they are exactly the same, not quite. The OEM uses a flat piece of aluminum sheet calculated to melt at 30 amp. You can convert to normal fuse for like $5 in parts.

I use like riding mower solenoids, priced around $15-$20 instead of $80 and work fine but you have to mount and wire it yourself. Easy.
 
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