Take the plug out and try again.
Engine spins rapidly every time = decompressor problem
Liquid fuel blast out of plug hole = carb float problem
No change = electrical problem
Run a jumper directly from the battery + to the starter motor.
motor spins quickly = solenoid or heavy solenoid wiring problem
No change then run a jumper from the battery - to the drain plug ( or other good ground near the starter.
Starter spins freely = ground connection problem
no change = faulty starter.
Some starters have rebuild kits for the brushes some don't.