When I turned they key to the ON position, I could hear the click from the fuel shut off solenoid, and when the key turned to START, the tractor started fine. But occasionally there was no click from the fuel solenoid, and when key turned to START position, tractor did not run just as expected. I removed the solenoid from its position on the engine and checked its operation. With the wires still connected to the solenoid and the body of the solenoid touching the tractor for ground. The solenoid clicked every time when key turned to ON and then a click when OFF. I repeated this step many times and it never missed a click. But when the solenoid was bolted back on the engine, the solenoid would not produce consistent clicks. Kind of hit and miss. When I did not get a click, I tapped the solenoid lightly with a screwdriver, got a click and the tractor started. The ground connection is good. Sometimes after getting no click, I just let it the tractor sit for a while, then turned the key to ON, got a click and the tractor started fine. Can you explain to me what possibly caused this kind of inconsistency? Does this have something with the replay or the OPC timer, something that I do not understand. Many thanks in advance for your help.