Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Engine has electric solenoid in the base of the carburetor. It has to have 12 volts, to stay open. It plugs the main jet when it closes. It may be loosing voltage or it may be getting overheated and shutting down. When you disengage the blades, the voltage load is less and the voltage likley goes up.
Did you see my response? Did you check the solenoid?