GENERAL INFORMATION
Page 1C-12 90-828631R3 MARCH 1999
Trim Tab Adjustment
Propeller steering torque will cause your boat to pull in one direction. This steering torque
is a normal thing that results from your outboard not being trimmed so the propeller shaft
is parallel to the water surface. The trim tab can help to compensate for this steering torque
in many cases and can be adjusted within limits to reduce any unequal steering effort.
NOTE: Trim tab adjustment will have little effect reducing steering torque if the outboard is
installed with the anti-ventilation plate approximately 2 inches (50mm) or more above the
boat bottom.
Operate your boat at normal cruising speed, trimmed to desired position. Turn your boat left
and right and note the direction the boat turns more easily.
If adjustment is necessary, loosen trim tab bolt and make small adjustments at a time. If the
boat turns more easily to the left, move the trailing edge of trim tab to the left. If the boat turns
more easily to the right move the trailing edge of trim tab to the right. Retighten bolt and
retest.
a
a - Trim Tab
Compression Check
1. Remove spark plugs.
2. Install compression gauge in spark plug hole.
3. Hold throttle plate at W.O.T.
4. Crank the engine over until the compression reading peaks on the gauge. Record the
reading.
5. Check and record compression of each cylinder. The highest and lowest reading
recorded should not differ by more than 15% (see example chart below). A reading
below 120 psi might indicate a total engine wear problem.
Example of compression test differences
Maximum (psi)
Minimum (psi)
180 162
150 127.5
6. Compression check is important because an engine with low or uneven compression
cannot be tuned successfully to give peak performance. It is essential, therefore, that
improper compression be corrected before proceeding with an engine tuneup.
7. Cylinder scoring: If powerhead shows any indication of overheating, such as discolored
or scorched paint, visually inspect cylinders for scoring or other damage as outlined in
Section 4 “Powerhead.”
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