3. INSPECTION/ADJUSTMENT ATV 300/250 Timing Hole Cap Index Mark IGNITION TIMING The ignition unit is not adjustable. If the ignition timing is incorrect, check the ignition system. Remove the timing hole cap. Check the ignition timing with a timing light. When the engine is running at idle speed, the ignition timing is correct if the "F" mark Timing Hole on the flywheel aligns with the index mark on the right crankcase cover. Compression Gauge CYLINDER COMPRESSION Warm up the engine before compression test. Remove the spark plug. Insert a compression gauge. Open the throttle valve fully and push the starter button to test the compression. Compression: 16 kg/cm (1600 kPa, 227 psi) If the compression is low, check for the following: - Leaky valves - Valve clearance too small - Leaking cylinder head gasket - Worn piston rings - Worn piston/cylinder If the compression is high, it indicates that carbon deposits have accumulated on the combustion chamber and the piston head. 3-8