EXAMPLE: An engine running at an elevation of 8,000 feet will have over a
30% power loss while a loss of engine power on a hot and humid day could be
as much as 14%. These losses apply to normally aspirated and supercharged
engines.
Compensating for power robbing conditions:
• Switch to a lower pitch propeller.
• Change the gear ratio if it is available.
Some boat performance can be improved by dropping to a lower pitch
propeller, but engine performance will still remain lower. In some cases, a gear
ratio reduction may be more beneficial. To optimize engine performance, prop
the engine to allow it to operate at or near the top end of the recommended
maximum RPM range at wide‑open throttle with a normal boat load.
Other advantages to propeller or gear ratio changes:
• Reduces the possibility of detonation
• Enhances overall reliability and durability of the engine
Setting Trim Angle while Running Engine at Idle Speed
The exhaust relief hole on the outboard can become submerged on some
boats if the engine is trimmed full in while running at idle speed. This may result
in exhaust restriction, rough idle, excessive smoke, and fouled spark plugs. If
this condition exists, trim outboard up until exhaust relief hole is out of the
water.
a - Relief hole submerged (wrong)
b - Relief hole above waterline (correct)
Operating in Shallow Water
When operating your boat in shallow water, you can tilt the outboard beyond
the maximum trim range to prevent hitting bottom.
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