2000 craftsman mower with 17 horse engine starts to spin but locks up can be turned by hand can be jumped with truck cranks with extra power but is hard on starters need help

Hi.
You did not tell, but I would bet it is a Briggs Intek. Good tutorial on adjusting valves on YouTube.
YouTube - Lawn Mower Repair Valve Adjustment
Cannot claim to be the first to post this here, or that I do it the way shown; but do acknowledge that it works.
Peace,
Clarke