LOWER UNIT - 6C-790-817643R1 DECEMBER 1996
SETTING OUTBOARD MOUNTING HEIGHT ON
BOATS WITH FLAT BOTTOM HULLS
1. Place (center) the outboard on the boat transom so
that the transom brackets are resting on top of the
transom. Temporally fasten the outboard to the
transom using two C-clamps.
2. Position the outboard in a vertical position.
3. Place a straight edge (a) along the bottom of the
boat as shown and measure the distance between
the bottom of the boat and top front edge of the wa-
ter intake housing (b).
b
a
a - Straight Edge
b - Top Edge of Water Intake Housing
4. Raise The outboard up on the transom the dis-
tance measured in Step 3. Use a straight edge and
recheck the mounting height. The top edge of the
water intake housing should be in line with the bot-
tom of the boat as shown.
5. Fasten outboard to the transom at this height.
Water testing
Checking for Cavitation
Making the initial outboard height setting should be
close to the optimum setting for the outboard. However
because of the hull design of some boats, obstructions
or imperfections in the hull ahead of the water intake
may require this setting to change in order to prevent
cavitation at running speeds.
When operating the boat, the outboard drive shaft
should be vertical when planing or tilted toward the
boat in order to provide a scooping angle on the water
intake. Tilting the outboard out beyond a vertical posi-
tion reduces the scoop angle and can cause impeller
slippage and cavitation. If the angle of the boat tran-
som does not allow the drive shaft to be positioned ver-
tical a Wedge kit should be installed behind the tran-
som brackets to increase the tilt-in angle.
NOTE: Slight cavitation in sharp turns and rough water
is acceptable but excessive cavitation is harmful to the
outboard and should be avoided.
Test run the boat. If cavitation occurs (air enters the
pump causing loss of thrust, engine over-speeds errat-
ically). the first thing to try is lowering the outboard
height 1/4 in. This can be accomplished by elongating
the drilled mounting holes in the boat transom by 1/4
in.
If cavitation still exists after lowering the outboard 1/4
in., it maybe helpful to seek advice from the boat
manufacturer.
A number of other options are available to further re-
duce cavitation.
1. Water intake fin kit (a) – Available from the Special-
ty Mfg. Co. for jet models 30 thru 140. The purpose
of these fins is to ram more water into the intake
and shield the forward sides of the intake from the
entrance of air. This kit will help reduce cavitation
when running with the wind in a chop.
a
a - Intake Fin Kit
Water Intake Fin Kit Part No.1186 for jet models 45
thru 140 and Part No. 1185 for jet model 30 is
available from.
Specialty Mfg. Co.
2035 Edison Ave.
San Leandro, CA 94577
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