If the fuel to air mixture is not correct then when a load is put on the engine it will die. IE: blade being engaged or transmission engaged. It can happen in any Carbureted Engine. The Carburetor needs to be pulled apart and the Jet cleaned with a very fine wire. Then spray out the carburetor with carb cleaner and an air compressor. Run SEAFOAM through the system to clean out any old fuel. Make sure the fuel used is new and clean. Inspect all belts to see if they are not over tightened and causing the engine to stall.