Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Welcome to JUST ANSWER small engines, let me try to help you !! I don't know it all, but maybe together we can get you a satisfactory answer!
Not much shown on the engine..What does the engine kill look like? Engine kills with key? If it does, it has electric fuel shutoff solenoid, usually just to the left of the injection pump body. This solenoid may not be opening when it needs to. Locate it, and when engine will not start/rev up, loosen it and slip it back, to see if engine will run. If engine runs ok, the solenoid is sticking.
Looks something like this on a Kubota.