Ken,
The solenoid does two things: it closes a circuit that can flow lots of amps to the starter motor, and it sounds like your solenoid is doing that. So the little gear spins like crazy. But it spins in the air because the other thing solenoids do is lever the little gear against the “flywheel” or some gear that is attached to the crankshaft - that’s what turns the engine. Your separate solenoid is not doing that. Close but no cigar.