2000-2005 Yamaha F40B Outboard Service Manual, Page 110Get this manual
1POWER UNITCOOLING SYSTEM Measuring steps (1) Remove the lock plate from the engine stop lanyard switch on the remote control boxtiller handle(2) With the throttle wide open, crank the engine setting the main switch in the START position until the reading on the compression gauge stabilizes6Remove: Compression gauge
7Install:
Spark plug(-s)