Not sure

[wnewton39]

can a starter seem to be working great when on the bench but draw down battery and not make engine spin enough
to start when back on motor ?

 

[bertsmobile1]

Yes.
With no load it will spin faster and draw fewer amps.

Question is why do you want to know this ?
Most times a starter that appears to be working off mower but will not work on mower is due to badly adjusted valves.

 

[Rivets]

I would also check you connections. A bad ground many times is diagnosed as a bad starter. Measure battery voltage when the starter is mounted on the engine and the key in the start position. If you battery is good and you have 11+V, starter is good and you have other problems, like valve clearance.

 

[redmondjp]

The starter could have a partially-shorted armature. It will spin no-load fine, but will not take a full load because it has greatly reduced torque.