Firstly, you’ll need to ensure your lawn mower is parked on a flat, even surface. The parking brake must be on and the ignition must be off. For safety, you must also ensure that the PTO switch is in the "off" position. As the lawn tractor engine ages, the PTO clutch can start ...
use a machined billet aluminum starter pulley on the crankshaft PTO end, then use a 2 wheel remote starter cart with an automotive or tractor starter motor with a V-belt pulley, high amperage push-button [starter] switch and an automotive 12 volt battery motor to crank the engine to start...