ignition

[Morala]

hope someone can help,i started the bike, 1974 550 today but when i pushed the starter button the starter kept turning over even when i turned the key off it just kept turning over until the battery ran down, never did this before so am at a loss as to what the cause could be any advice would be much appreciated cheers.

[McCabe-Thiele (Ted)]

Sounds like a stuck solenoid unit.

[Bryanj]

I agree, duff solenoid

[Martin6]

The spring in the starter button can stick and the nylon type plastic can wear, resulting in the contact not breaking. I noticed a strange whirring noise when i was riding, starter was spinning while the engine was running and traced it to this.. Be very careful dismantling it, if you think that might be your issue. The spring and ball bearing like to fly off.

Edit: just thinking. This can't be the problem, as the starter would stop when the ignition is off. I don't see how your starter still spins with the ignition off, unless you have a short in the circuit, bypassing the ignition switch.

[Sesman]

I reckon the solenoid plunger and copper contact bar is sticking when engaged. It’s an easy fix.

[Bryanj]

Just realised that this is a us 550 and in these the plastic contact assembly inside the rh switch can degrade and crack.
On these the button turns off the headlamp before making starter contact so it is possible that if the assembly breaks the starter contacts could be permanently contacting

[McCabe-Thiele (Ted)]

Should be easy enough to disconnect the small wires to the solenoid to identify if it's the power to the solenoid circuit causing the issue or if the solenoid itself has faulted.

[Sesman]

I’m not sure it can be the button mechanism as the owner has stated that killing the ignition didn’t stop the starter turning. I suspect it’s a mechanical problem with the solenoid plunger and copper contact bar.

[Sesman]

There is also some potential for collateral damage here. If the battery was healthy and continued to run the starter until fully discharged, not only may the battery be damaged, but the starter motor windings could also be damaged due to overheating.🥵

[Bryanj]

Kill switch only stops coil circuit not the starter circuit

[Sesman]

I don’t quite understand that. You can start the bike with the ignition off?

[Martin6]

Kill switch only stops coil circuit not the starter circuit

Not the kill switch, he's turning it off with the ignition key switch.

Very odd you're getting constant power to the starter and it continues with the ignition switch off. Starter earth should be straight to the battery? So, to me, your problem is in the switched live. I can't think how you're getting a connection to battery positive down there that bypasses the ignition switch and the handlebars starter button. Do you have a stock wiring loom?

So difficult to trace remotely. Study your wiring diagram and trace how the starter gets power. Then it's a meter, to test the circuit. As you'll need the bike's battery connected, maybe disconnect the starter, to look after it and hook the terminal wires up to a bulb, maybe what you use to set points timing?

[Sesman]

The solenoid switch contacts posts are permanently live, being fed directly from the battery. The starting current is circa 110A. The ignition switch is fed directly from the fuse box and the fuse box is fed from the starter solenoid switch contact. Basically the entire electrical system is fed from battery, to solenoid contact post, to fuse box then to the ignition switch. The switched side of the ignition feeds the starter button and the coils. Basically, if you depress the starter button, the coil engages and although you may stop pressing the button, if the solenoid post within the solenoid jams in the closed position, it will continually run the starter regardless of the ignition position.

[Sesman]

I’ve just been in the garage to check. Turning the ignition off when depressing the starter stops the starter.

[Sesman]

Morala.

As a starter(pardon the pun), I recommend you remove and open the starter solenoid. Check to make sure the post moves freely and that the horizontal copper bar is not fused across the solenoid contact posts. If necessary you can flip the bar over to provide a nice set of fresh contacts.