You've got some internal starter problems- - - -possibly shorted windings in the armature and/or worn bushings that are allowing the armature to drag the pole shoes. Once the compression load goes onto the starter it slows down.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!