Topic: Starter button not igniting the starter

[ScottB]

I picked up my latest project tonight, a 73 750 and have two issues:


1) Starter button won't fire up the bike.  I did a search with no luck.  I traced the green/red wire to the Safety Unit Starting Motor and it lights up going into the unit when the button is pressed.  Should a wire coming out of it light up too?  Would this mean that the Safety Unit is shot?  Is there a way to diagnose it?

2)  The PO says the when the bike did run it ran on two matching cylinders, 1,4 or 2,3.  Can I pull the coils off a 500 I have to see if that is the issue?

Thanks for the input, I appreciate the help. 

[SteveD CB500F]

To check the starter solenoid, short out the input to ground (to replicate the action of the button). The solenoid should click and the starter should run. If not, suspect wiring from the button.

To test the starter itself, short the power feed directly (use a BIG screwdriver and don't leave it on for long)

Duff coils are very rare. It's more likely to be the ignition wiring on the 12V side.  Swap the 12V feeds over to test. As the system uses "wasted spark" it won't make any difference to the running of the engine.

[ScottB]

I checked the starter solenoid before I posted and it kicks the starter fine.  I'm wondering if the Safety Unit can go bad.  Does the green /red wire that feeds into the unit trigger a wire to be hot coming out of it?

I'm not sure what you mean by checking the 12v side of the ignition.  Please break it down to me crayon and paper style.

[SteveD CB500F]

By the 12V side I mean the circuit from the ignition switch to the points to the coil. Each set of points makes/breaks the 12V circuit, causing the coil to produce the high voltage for the spark.

In my experience, wiring faults here are very common, especially between the points and the coils.

[bryanj]

BE CAREFULL There are two different ways of making the solenoid work!!!

The early ones had a permanent "live" wire and the other wire was grounded via the handlebar button---Usually a yellow/red wire and NO safety circuit

The later ones had a permanent "ground" and were fed power via the button and safety unit.

The safety unit will only let power through when either the neutral light is on OR the clutch lever is pulled in and is normally an incredibly reliable unit as its purely an encased diode, Then again anything CAN fail eventually.

Trace the wires comming out of the safety switch and one of them should be the same colour as a wire on the solenoid so if you temporarily connecr the green red to that you have bypassed the safety unit and can test the rest.

[ScottB]

Steve, thanks for clearing that up.


Bryan,
I have checked the wiring.  The yellow / red is always hot that comes out of the Safty Unit and goes to the solenoid.  The green / red is still getting hot when I press the button.  It looks like I have the harness that doesn't ground at the handle bar point.

[Rsnip988]

the prob could just be the contacts on the button itself, they are known to get corrupted

[mic-57]

The clutch switch bypasses the safety unit. If the button wont work with the clutch lever pulled in (assuming the clutch switch is good) than the starter button is bad.

[fuzzybutt]

with my 74' 750k the black wire coming off the starter solenoid is hot, yellow/red is grounded when the switch is hit, however the new harness i have has the plug to wire a safety relay in. the plug has a yellow/red, green, light green/red, dark green/red and a black wire in it. which ones do i need to jump across to get the starter to work is my question.