Starter not dis-engaging

[sauce]

I have a starter issue with my '77 CB750A.  As soon as I turn the ignition switch (key) to the "on" position, the starter starts to whirl.  Pressing the starter button does not stop it (although it has in the past).  When I click the bike into first gear, the starter winds down, but it starts again whenever I put it back into neutral.

I thought the solenoid was bad, and took it apart and cleaned it.  This didn't work.

Any other suggestions?

[Re-run]

Have you cleaned the button? They sometimes fall apart and it could be making contact.
Otherwise, I have not had that happen but something has to be sending power to the starter so it has to be electrical.
Have you downloaded the auto manual here?

[sauce]

I've not cleaned the button, though I have sprayed it will electrical cleaner.  Didn't seem to help, though I might have to dig it out and take it apart.

I have a manual -- thanks for the link.