Drilling Outboard Mounting Holes - Mercury 150 FourStroke Operation & Installation Manual

1. The outboard should be mounted high enough on the transom so the
exhaust relief hole will stay at least 25.4 mm (1 in.) above the waterline
when the engine is running at idle speed. Having the exhaust relief hole
above the waterline will prevent exhaust restrictions. Exhaust restrictions
will result in poor performance at idle.
2. Add 12.7 cm (5 in.) for XL models to the listed outboard mounting
heights.
3. The mounting height of the outboard must not exceed 63.5 cm (25 in.)
for L models, 76 cm (30 in.) for XL models. Mounting the outboard higher
may cause damage to the gearcase components.
Increasing the mounting height will usually:
• Reduce steering torque
• Increase top speed
• Increase boat stability
• Cause propeller to break loose during planing

Drilling Outboard Mounting Holes

IMPORTANT: Before drilling any mounting holes, carefully read Determining
Recommended Outboard Mounting Height and install outboard to the
nearest recommended mounting height.
1. Mark four mounting holes on the transom using the transom drilling
fixture.
a
c
OUTBOARD INSTALLATION
NOTICE
b
2757
a - Drill guide holes
b - Transom drilling fixture
c - Transom centerline
a
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