I just bought this troy built zero turn it has a briggs and Stratton twin cylinder motor but I don't know what horsepower it is anyway when I go to start it it turns over a couple of rounds and then it just stops like it is locked up but sometimes it will turn over more than two rounds before it does it You can reverse the flywheel the opposite way and it want lock up

SOURCE: Starter energizes, won't turn engine.

your battery is in a weak state also the solenoid is shorting out replace the solenoid

SOURCE: Troy-Bilt Briggs & Stratton 550 restarting

Troy, Unless you are using old fuel (it breaks down after 1 week) it sounds like you have a faulty spark plug. Replace this first, drain any old fuel and replace with fresh fuel (premium unleaded). A faulty plug will work one minute but then fail like you have described.

SOURCE: I NEED A DIAGRAM OF A BRIGGS AND STRATTON TROY

Go to link below for a parts break down for your tiller. Starts on page 23

http://dl.owneriq.net/c/c23c1d7c-74ff-4347-b31e-a0ee0462b35e.pdf

SOURCE: MTD Model #13506756336 Ser #1A115C50008 16 HP

Possible faulty "operator presence relay" #1

SOURCE: 18hp twin cylinder Briggs & Stratton backfire

Check to see if the carb is clean, if so the anti diesel value could not be working. Apply 12 volts to value and see if it move's. If that works then you may what to check the fuel pump and see if it pumps. After you tried all that then you may have change the main jet size because these engines come with a small jet for the EPA.