Troubleshooting a Toro lawn and garden tractor is not a hard task to accomplish if the troubleshooting sequence is properly carried out. The important part is that each procedure (step) be fully executed - thus eliminating some reasons for the malfunction. By process of elimination, most common problems can be identified in less than an hour by a moderately skilled homeowner.
Park the tractor on a flat level surface, and engage the parking brake. Start the engine. If the engine will not start, make sure the PTO is disengaged all the way, and that the parking brake is engaged and the operator is sitting on the seat in the correct position. Be sure that all components of the Toro safety interlock system are in the correct position (user manual will help with this).
Check that the battery was installed with the negative terminal attached to black ground wire, and the positive terminal attached to the red wire. Check the water level in the battery, then charge the battery until it is fully charged with an automotive battery charger. Remove the battery cables from the battery terminals and clean the battery terminals with a wire brush to remover corrosion. Reattach the battery cables.
Tighten the engine ground wire running from the engine to the frame. Check for loose wiring connections in the fuse box, and wire harnesses. Tighten all loose connections. Verify that all fuses are good (not blown or burnt).
Replace the gas in the fuel tank with fresh gas. Clean the fuel filter and check for adequate flow from the fuel lines. Clean or replace the air filter. Clean or replace the spark plug, making sure the spark plug gap is correctly set (specific gap may be found in the user manual). Make sure the spark plug wire is firmly attached to the spark plug.
Start the engine. If it runs rough or smokes excessively after a 5 minute warm up period (without the mower engaged) the engine needs a tune up. If the mower only runs rough when in the mowing configuration, then the PTO belts and mowing deck need some adjustments.