2004 SR Johnson 2 Stroke 9.9, 15, 25, 30 HP Outboards Service Manual, Page 39Get this manual
INSTALLATION AND PREDELIVERY TRANSOM MEASURING AND DRILLING Use this procedure to determine whether or not the boat's transom height is correct for the outboard's shaft length: Lift the outboard using the lift grips (NOT the tilt grip or steering handle) and place it in the center of the boat's transomThe resulting position of the antiventilation plate must be no higher than the boat's bottom and no lower than in(5.1 cm) below itIf the resulting position of the antiventilation plate is above or below the to in(0 to 5.1 cm) range, the engine shaft length must be changed or the boat's transom must be modifiedIf you install and operate the outboard: Lower than recommendedSerious powerhead damage could result from water entry into the lower engine cover or overloading from an under-revving propeller at wide open throttle Higher than recommendedSerious powerhead damage could result from inadequate cooling or an over-revving propellerPropeller ventilation (slippage) often occurs, resulting in poor boat performanceDR31712