2001 Edition Yamaha F225A and LF225A Outboards Service Manual, Page 111Get this manual
Power unit Checking the compression pressure
1Start the engine, warm it up for minutes, and then turn it off2Remove the clip from the engine shut-off switch on the remote control box3Remove the ignition coil cover and all spark plugs, and then install the special service tools to each spark plug holeNOTE: If the compression pressure increases, check the piston and piston rings for wearReplace if necessary If the compression pressure does not increase, check the valve clearance, valve, valve seat, cylinder sleeve, cylinder head gasket, and cylinder headAdjust or replace if necessary
Checking the oil pressure
1Place rag under the oil pressure sensor2Remove the intake silencer and oil pressure sensor, and then install an oil pressure gauge to the oil pressure sensor installation hole
CAUTION:
Before removing the spark plugs, blow compressed air in the spark plug well to clear out any dirt or dust that may fall into the cylinderCompression gauge 1: YU-33223-1 Compression gauge extension 2: YB-06563 4Fully open the throttle, crank the engine until the reading on the compression gauge stabilizes, and then check the compression pressureMinimum compression pressure (reference data): 880 kPa (8.8 kgfcm2, 125 psi) 5If the compression pressure is below specification and the compression pressure for each cylinder is unbalanced, add small amount of engine oil to the cylinder, and then check the pressure again