2004 John Deer Buck Utility ATV 500, 500EX and 500EXT Service Manual, Page 40Get this manual
Replace defective part(s) (ex piston, ring(s), etcGo to next stepValve seat worn andor damaged? Repair by performing valve guide procedure (refer to "Cylinder and Head")Readjust valve clearance Check if cooling system shows any failure (see "Cooling System")System is leaking? Repair andor replace damaged part(s)Go to next stepCheck oil levelOil level is to high? Drain and refill with appropriate oilGo to next stepCheck condition and heat range of spark plugMelted spark plug tip or inadequate heat range? Install recommended spark plugGo to next stepCheck calibration of carburetorWrong carburetor adjustment (engine too lean)? Clean and readjust carburetor
Air filter is clogged due to contamination? Replace air filterGo to next stepCheck spark plug condition andor gapFouled spark plug or wrong spark plug gap? Readjust gap and clean spark plug or replaceGo to next stepCheck spark plug typeImproper spark plug heat range? Install recommended spark plugGo to next stepCheck engine compression and perform engine leak testRefer to "Engine Leak Test" procedureCheck for possible piston seizureDamaged head gasket andor seal andor leaking inletexhaust valve(s)? Replace andor repair defective partsGo to next stepWorn piston andor piston ring(s)? Replace (refer to "Cylinder and Head")Go to next stepCheck for water in fuel (wrong fuel)There is water in fuel or wrong fuel? Drain fuel system, search for leakage and refill it with appropriate fuelGo to next step