99 b2300 4cyl manual. Just changed starter. Now when I hook up the battery the starter runs on its own and just turns the motor.

 

Check your starter connections to ensure that the solenoid wire isnt touching the main power. ..I assume that this isn't the reason you changed the starter

 

When you mean just turns the motor you mean it just turns the starter and not the engine?

If this is the case you wired it in such a way that the solenoid is bypassed.

The solenoid is the high current switch of the starter and also actuates the bendix forward to engage the flywheel.

Can you take a pic of your connections at the starter?

 

Starter solenoid on the fender could be stuck....