Problems When Starting
If the engine on your John Deere 425 riding mower is difficult to start or will not start at all, the spark plug is possibly dirty or damaged, the spark plug gap is set incorrectly or the spark plug wires are broken or loose. If the PTO switch is in the “On” position or the brake pedal is not depressed, the engine will not start. Stale or contaminated fuel or a dirty fuel filter also causes difficulty in starting the engine.
Problems When Running
Stale or contaminated fuel could cause your John Deere 425 riding mower to idle rough or to miss under a load. A dirty or damaged spark plug or incorrect spark plug gap setting can also cause these problems. An engine that runs unevenly might have a clogged fuel filter or air cleaner element. Other reasons for uneven running are loose electrical connections or stale or contaminated fuel. If the engine coolant or oil is low, the engine can overheat. Plugged engine air intake screens or radiator fins also cause overheating.
Transmission Problems
If your John Deere 425 riding mower will not move forwards, backwards or either way while the engine is running, the transmission is possibly defective. Damaged or broken traction drive belts or pulleys will affect the operation of the transmission. The free wheel valve on an automatic or hydrostatic riding mower should be pushed in for proper mower operation.