Electrical issues and starting...

[choptrees]

I have a 1975 GT550 with 20000 kms on it. Found on the side of the road in decent condition a couple of years ago. It had a broken piston, so ripped the bike apart, replaced piston, new rings, replaced crank seals, balanced the crank, honed the cylinders, and put it back together. Now getting around to the starting phase which I imagined would be entertaining and it is!

Today connected a battery up to the bike and the first few kicks showed I had spark at two plugs and the gear position and neutral lights worked. Then something started to smell funny and I lost the neutral light, gear position light, and spark. Then with ignition on I noticed that when I pulled the clutch in it was arcing between the lever and the metal on the rest of the clutch lever mount. I tested the voltage of the engine cases, same voltage as the battery... Bad ground... I undid all the wire connectors and replaced them one by one until I found the cause of the bad ground. When I plug the rectifier in the engine casing is electrified. The rectifier is off a spare, or maybe it's just completing a circuit?

So, two questions... Where on earth are the fuses? And anyone seen a problem like this before? Cheers!

[jabcb]

Here is the wiring diagram:
download/file.php?id=824

The bike uses a single inline fuse that protects the battery from shorts.

Check the wiring for the alternator & starter.
You may have pinched a wire & have a short.

[Coyote]

The fuse is in the heavy red lead coming off the + terminal of the battery. A single 20 amp fuse.Those old fuse holders can cause all sorts of nightmares all by themselves. It's advisable to cut out the ancient fuse holder and solder in a modern blade type fuse holder. Here in the US they are available at Ace Hardware.
Also there is a heavy ground strap that runs from the battery - terminal to the engine case, normally to a bolt near the kick starter. Is that missing?

[choptrees]

The fuse is in the heavy red lead coming off the + terminal of the battery. A single 20 amp fuse.Those old fuse holders can cause all sorts of nightmares all by themselves. It's advisable to cut out the ancient fuse holder and solder in a modern blade type fuse holder. Here in the US they are available at Ace Hardware.
Also there is a heavy ground strap that runs from the battery - terminal to the engine case, normally to a bolt near the kick starter. Is that missing?

The red lead from the battery is quite short, doesn't look like there'd be room for a fuse in there. There's another red wire that comes off the starter solenoid that is thinner and in this bike a previous owner is clipped this wire a put a restrictor in it. The heavy ground strap is there but not in great condition. I've put jump leads between the battery connections and the bike, I can up clip to problem solve without having to disconnect a battery constantly!

[Vintageman]

The clutch lever sparking. I assume engine not running now or maybe it is?

If the spark is more than just a brief spark like walking across as carpet touching a door knob, you have a short: Batt voltage is flowing into little or no resistance back into batt ground (if not running most likely) or similarly alternator energy running into a short.

It sounds like when you first put in batt with engine not running all OK. Then you started engine, then smelt something get hot?

If so my guess is the engines charging system was charging into a short, that short opened the connection (ground) between batt, support circuitry and engine charging system.

So look for burnt connections or even open I suppose. Look for wires improperly connected when compared to diagram. If wiring routed OK, but you found something burnt (maybe even to a point it is an electrical open), Then you should question various components (e.g. regulator) for a potential short. If the fuse from batt did not blow, and was a short, I think the source of energy is the Alternator into ground. If it blew and problem could be either shorted? Good batt correct?

So guessing of course but, root cause may have been a short not the open

[Coyote]

The wire with the fuse plugs into the bullet connector shown. Follow that wire and you SHOULD find the fuse. The other wire with the black cap goes to the starter solenoid / relay.
I wonder what the resistor is for? I hate PO 'fixes'.

[Coyote]

a previous owner is clipped this wire a put a restrictor

I see you used the word restricor and not resistor. Ate you possibly looking AT the fuse holder?

[jabcb]

There's another red wire that comes off the starter solenoid that is thinner and in this bike a previous owner is clipped this wire a put a restrictor in it.

Take a close look at the "restrictor". Should actually be the fuse.

[Coyote]

Take a close look at the "restrictor". Should actually be the fuse.

My thoughts exactly.

[choptrees]

The saga continues... I've checked the system with a volt meter. I've got 12 volts at the alternator, at all three points, after the fuse (not a restrictor!), and inline going to the wiring inside the headlight. I don't see any burnt connections, and the engine casings are no longer charged. However, no spark in any of the plugs. Could be points? But I had spark before I started having problems. Could it be the run switch? Or coils? One thing I should point out as well. I changed from a denso system to a kokusan. I changed the rectifier, the alternator, starter... Anything I missed? I still have all the original denso system, so could change back. The only reason I did this was the starter motor teeth are starting to look a little hooked. Any suggestions?

[jabcb]

Check voltage drops in the ignition system with the points open & closed.

[Suzukidave]

With the ignition switch on you should be getting 12v ( or close ) at the orange wires going to the coils .

[choptrees]

Thanks for the tip. I believe I was getting around 0.11 volts at those orange cables. I disconnected them and tested the voltage coming from the battery, rather than from the coils! I'm assuming though that each set of points needs to be closed to transmit voltage to the coil and then onto the plug?

[jabcb]

The power goes from the battery to the coil orange wire, and then from the coil to the points.

You should have close to 12v at the orange wires going to the coils.
(multimeter leads connected to orange wire & battery negative)

Voltage drop across coil depends on the points.
(multimeter leads connected to the two coil wires)
With the points closed it should be close to 12v.
With the points open it should be about 0v.

[choptrees]

I have 12 volts before and after the coils. Still no spark. Not sure where to go now. Thanks.