New starter just spinning - what am I missing?

Given that I've been out in an unheated garage for the last four hours, I hope you'll collectively forgive what is probably an incredibly basic question; my brain just isn't firing at the moment.

In the course of doing a bunch of work on my 2002 I decided to replace the old starter. It worked, but slowly, so as long as I had access I figured why not. Tried to crank it over today and the new starter just spins - it spins fast, but doesn't engage the flywheel. Assuming this means the solenoid wasn't working properly, I pulled it out and bench tested it - the solenoid snaps forward and the gear spins just fine on the bench.

Checked gear diameter and depth - both match the old starter exactly. It's wired just like any traditional starter: big wire from the battery, little wire from the ignition to the solenoid.

What the hell am I missing here?

Ive had a few starters on small motors that would do the same. The bendix needed a spacer to get it to grab the worm gear, then it would engage right every time. The ones i had were on OEM starters on kawasaki motors(thanks for nothing kawasucky). 

But it pops up on the bench?

Did it find a missing tooth on the flywheel? 

Nope, flywheel is good. Solenoid pops vigorously and immediately on the bench.

hooked the power wire to the wrong post? i've done that before where as soon as i get in the car, key on - boom starter is humming away lol.

If you hooked the solenoid wire to the big terminal that goes out of the solenoid and into the starter you'd get rotation but no popping out. If you leave the big wire off the starter and only have the small wire hooked up and try to crank it it should give you a solid clack of the gear popping out.

Vigo said:

If you hooked the solenoid wire to the big terminal that goes out of the solenoid and into the started you'd get rotation but no popping out. If you leave the big wire off the starter and only have the small wire hooked up and try to crank it it should give you a solid clack of the gear popping out.

I think this must be what's going on. There are two male spade terminals, one connected to the big terminal and one to the solenoid. The latter is hidden from view from above when the starter is mounted - I'm reasonably certain I stuck the connector on the visible terminal, which is of course incorrect. I'll go back at it tomorrow and see if I can get things working properly. Thanks.

Just to wrap this up, the problem was the wire on the wrong spade terminal. With the starter reinstalled and the wiring hooked up correctly the engine spun up immediately. Thanks again.