3A-1990-13645--2 495 FUEL SYSTEM AND CARBURETION
IDLE SPEED ADJUSTMENT
Adjust engine idle RPM as outlined in Section 2C
“Timing/Synchronizing/Adjusting”.
MAIN (HIGH SPEED) JET ADJUSTMENT
The carburetor is equipped with a fixed high speed jet
and normally no adjustment is required. However,
extreme changes in weather (temperature and
humidity) and/or elevation may result in a too lean or
rich fuel mixture at wide-open-throttle, which may
require a change in the high speed jet. A smaller size
main jet will lean the fuel mixture, and a larger size jet
will enrichen the fuel mixture.
20365
STANDARD HIGH SPEED JET CHART
Model
Carburetor
Number
Main Jet
Size (inch)
Bowl Vent
Jet (inch)
70 WME-7 .072 .094
75 WME-8, 17 .068 .094
80 WME-9 .064 .094
90
WME-10
WME-19
.072
.066
.094
.094
100 WME-11, 20 .054 NONE
115 WME-14, 21 .076 NONE
REJETTING CARBURETORS FOR HIGH ALTITUDE
OPERATION
The carburetor jet installed at the factory is for engine
operation at sea level through an elevation of 5000
feet (1524m) above sea level. If the engine is to be op-
erated at an altitude higher than 5000 feet (1524m),
then it will be necessary to rejet the carburetors. Refer
to the jet chart following for jet recommendations at
approximate altitudes.
Normally, for every 1000 feet (304.8m) of altitude in-
crease, main jet size is reduced by 2%. However, this
does not always hold true for all situations; different
boat, motor, load and ambient air temperature condi-
tions may require different jets – I.E. – going a jet size
richer than recommended for a particular altitude may
improve acceleration. It may also be noted that no no-
ticeable improvement in engine performance was
achieved by changing the standard main jet at alti-
tudes up to 5000 feet (1524m). Above 5000 feet,
however, changing jets did improve performance.
Several additional changes to improve engine
performance at higher altitudes are as follows:
1. Idle timing should be advanced 2-3 degrees at
5000 feet (1524m) and above.
2. Prop engine at the top of the recommended RPM
scale +/–150 RPM.
3. Reset idle mixture screws for best idle. With stan-
dard idle mixture setting (sea level) considered to
be at the 12 o’clock position, adjust the mixture
screw leaner for all models as follows:
5000 ft.
(1524m)
7500 ft.
(2286m)
10000 ft.
(3048m)
1 o’clock 1 o’clock 2 o’clock
4. Change gear ratio:
Model
Above
5000 ft.
(1524m)
70, 75, 80, 90 – Std. Ratio – 2.33:1 None
Available
100, 115 – Std. Ratio – 2.08:1 2.33:1
HIGH ALTITUDE JET CHART
Model Carb Std. Jet
5000 ft.
(1524m)
7500 ft.
(2286m)
10000 ft.
(3048m)
70 WME-7 .072 .072 .070 .068
75 WME-8, 17 .068 .068 .066 .064
80 WME-9 .064 .064 .062 .060
90 WME-10
WME-19
.072
.066
.072
.066
.068
.062
.066
.060
100 WME-11, 20 .054 .054 .050 .048
115 WME-14, 21 .076 .076 .072 .068
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