It won't start but starter and solenoid OK

[Gord Baker]

Remove and clean all Battery and starter Cable connections. Use a file/wire brush etc.
With Car or other 12VDC source OFF, connect + to Starter and - to Clean solid surface on engine like mounting bolts.
Work backwards from there....other side of solenoid etc.
NEVER TRY TO BOOST A SMALL ENGINE FROM A VEHICLE WITH ENGINE RUNNING. YOU MAY DESTROY THE CHARGING STATOR ON THE ITEM.

 

[jshep1102]

have you checked your valve adjustment? I've had problems where loose valves make for extremely high engine compression that the battery/starter cannot overcome and it draws the battery down hard. If the battery stays at 12+ volts during the starting attempts, I agree with the previous recommendations to focus on the solenoid and/or cabling.

 

[Beamster]

Bad (new) solenoid?
I once had a starter gear jammed in the flywheel teeth and it reacted as you describe. The starter plunger would not retract so it took some coaxing to free it up then the system worked again. I have no idea why or how it happened.