2004 SR Johnson 2-stroke 40, 50HP Service Manual, Page 69Get this manual
MAINTENANCE SPARK PLUGS
Air Silencer
The air silencer minimizes audible noise related to air flow into the engineAdditionally, it collects any fluid residue that migrates from the leaf plate or the throttle body area
SPARK PLUGS
Spark plugs should be removed and examined periodicallyReplace worn, fouled or damaged spark plugsUse only recommended spark plugs with the correct gap settingModels 40 and 50 Recommended QL78YC 0.030 in(0.8 mm)
Remove spark plugs and inspect condition Set spark plug gap on new, replacement spark plugs