2005 Yamaha F90TR 90HP Outboards Factory Service Manual, Page 69Get this manual
POWR Power unit
Power unit
Checking the compression pressure
1Start the engine, warm it up for minutes, and then turn it off2Remove the engine stop lanyard from the engine stop lanyard switch on the remote control box3Remove the spark plug wire cover and all spark plugs, and then install the special service tools into spark plug hole
NOTE: If the compression pressure increases, check the pistons and piston rings for wearReplace if necessary If the compression pressure does not increase, check the valve clearance, valve, valve seat, cylinder head gasket, and cylinder headAdjust or replace if necessary
Checking the oil pressure
1Remove the flywheel magnet cover2Place rag under the oil pressure switch