I believe in doing the simple, aka "Cheap", tests first. So, try jumpimg the solenoid.
Turns Over
If it turns over then your problem is not the starter but somewhere in the circuitry before the solenoid, like the starter button (Quite possibly as a result of the handlebar changeout), or the solenoid itself.
Does Not Turn Over
If it does not turn over I would suspect the starter, the power to the starter from the solenoid, or a bad starter ground.