Mercury 8.1S Horizon, Product Applications Manual

Page: 157 / 163

Predelivery Preparation
Page 10A-4 90-863758060 AUGUST 2006
MIE Models Diameter or Pitch Change RPM Change
Gasoline 1 Inch 150
14394
Detonation Pre-Ignition
It is the responsibility of the boat manufacturer and/or the selling dealer to equip the power
package with the correct propeller. Select a propeller that will allow the engine to operate
at the maximum RPM of the engine's specified wide open throttle (WOT) RPM range. (See
Section 1 - Important Information for specifications). Use an accurate service tachometer
to verify RPM.
Example: Prop the engine as close to 4800 RPM as possible on an engine with a
specified WOT RPM range of 4400–4800.
When selecting the propeller, the boat should be loaded as outlined below. Weights can
be used to simulate the load. Loading the boat in this manner will help to ensure that the
RPM do not fall below the specified range when a heavy load is placed aboard by the
operator.
1. Half-full fuel tanks
2. Full water tanks (if equipped)
3. Four people in seats at helm and stern (equally distributed)
Equivalent Weights
1 gear 86 kg (190 lbs)
1 US gallon gasoline 0.72 kg (6 lbs)
1 US Gallon Water 1 kg (8.3 lbs)
Select model and initial pitch propeller to begin testing with using information provided in
the
Mercury Precision Parts and Accessories Guide. A vast array of propeller models and
pitches are available to suit virtually any boat application. Initial selection is typically done
by boat weight.
Operate boat at wide open throttle and adjust power trim to achieve optimum speed without
using excessive trim. If RPM is above the specified range, a higher pitch propeller must be
used. A lower pitch propeller must be used if RPM is too low. There is typically a 200–300
RPM change for every 2 in. change in propeller pitch.
NOTE: Engines are equipped with an RPM rev-limiter. The rev-limiter is set slightly above
the specified WOT range of the engine and is designed to help prevent damage from a
temporary excessive engine RPM condition. The rev-limiter must not be operated against
continuously. When rev-limiter is activated, the engine will appear to have a misfire. Once
the RPM drops into the specified operating RPM range, normal engine operation resumes.
On carbureted engines with Thunderbolt V Ignition, service (or boat) tachometer is not able
to give an accurate RPM reading when the rev-limiter is activated.