Topic: CB650 1979 Clutch diode smoke - back to diagnosing

[Xeleon]

Hi everyone!

So today was going to be the final day of my long fun project. The bike is looking amazing and with the brilliant help of BrianJ and Kerry with my electrical gremlins, I was all sorted and ready to hit the start button for the first time. Always a tense moment! Unfortunately, it didn’t go so well. All my fault though as I had the electrical a working before dissembling and routing all the wires etc.

So, what happened?

First, I connected the positive cable to battery and then the ground, negative. I had a few sparks but didn’t think much of it. After connection, I went to turn the key. Nothing. Nothing at all, and that is where I noticed that the 30A blade fuse in my starter solenoid had blown.

Rinse and repeat. Cables disengaged from the battery, I replaced the blade fuse with another 30A replacement fuse (maybe bad china quality?, but it was what I had at hand from another project). With the ignition off, I attached the ground cables to the battery (from frame and starter motor) and instead of bolting on the positive cable, I touched it on the positive battery terminal to see if I got sparks again, potentially blowing a fuse - but no! I thought I was all good for a split second until it started smoking. I quickly removed the cable to contain damage.

I noticed the smoke came from the clutch diode (see picture), so I removed the gas tank and examined the wires and socket. Nothing had melted, but the diode smells fried. While having the tank off, I noticed that my Black White connection on my left starter coil was not connected (see picture). Possible culprit?

I’m obviously puzzled to why the blade fuse didn’t blow on the second attempt. Was this just because of the order of which I connected the battery? So because of this, I started googling the connections of the starter solenoid, and I’ve realised that they might have been connected backwards. My starter solenoid does not have any B (battery) and M (starter motor) indications on the terminals. I know my 4 wire blade connector is connected properly with YellowRed on top left blade and GreenRed on top right blade. (See picture)

Based on this, can anyone shine light on what most likely has caused my fried clutch diode?

I’ll be ordering a new one - and possibly a new starter solenoid? What do you think?

Any input and help will be much appreciated. Just ask if you have any questions and I can elaborate or look into it.

Very appreciative!
Thanks :-)

[Xeleon]

Pictures

[bryanj]

That problem is just about impossible to long distance diagnose sorry, the diode should only be in the control circuit of the solenoid along with neutral light and switch i would have to search carefully my wiring diagrams to check but dont have acess for a while

[newday777]

Something definitely isn't wired properly on your bike. You had a direct short is why it happened. Either you have the wrong battery that has the positive and negative on opposite sides of where they should be (I ordered a new battery from a local shop, the young girl who ordered it didn't check that the positive was on the right side of the battery before she ordered it. I noticed it going to connect it on the bike, I gave her a call and she was apologetic and ordered the correct one).
Or your custom wiring is wrong and as bryanj says ,it is a hands on in person inspection time by someone local that knows wiring schematics to find the culprit.

Don't forget to oder a new bottle of smoke to fill the harness back up before you hook it back up.

[calj737]

Your fuse didn’t blow on the second attempt because you didn’t turn the ignition ON like the first attempt.

You stated the BLK/WHT wire form your starter motor… That wire pictured is for the Ignition Coils. Perhaps a typo? Regardless, that is a switched power wire and should NOT intersect a ground or the frame. It brings 12v to the coil when the key is moved to ON. This could well be your “short”.

[HondaMan]

Like BryanJ mentioned: I received a CB650 last summer to fix up, and it had the mirror-image battery in it, too. Make sure of the (+) and (-) terminals.

[Don R]

 A few years ago, Advance Auto had a bunch of batteries either made with the polarity wrong or their book was wrong. A guy had toasted his Sportster shortly before I refused the one that they handed me.

[Xeleon]

For the curious souls that might stumble upon the post looking for an answer.

Thank you guys for your input.

I managed to identify and fix the issue.

It was in fact the 4 pin blade connector that had been turned backwards. So looking at the pic perspective, the Yellow/red and Green/red had to point downwards instead of upwards. My clutch diode rectifier seemed to survive this time despite the smoke.

It was a simple wiring issue with the starter solenoid.

Got her started! With a few oil leaks, but nothing that can’t be fixed by tighting a few bolts and replace a O-ring.

Cheers!

[HondaMan]

Good sleuthing, and Happy New Year!