O.S. Engines 21RG-MX - Manual (Page 18)

7. Launch the boat and gradually open the throttle to
its fullest extent. If at this point, the engine puffs
out a good deal of smoke and does not accelerate
smoothly and rapidly, it is a sign that the idling
mixture is too rich. Therefore, turn the mixture
control screw clockwise 45 to 60
° . Repeat the run
and recheck the result.
8. If, on the other hand, the idling mixture is too lean,
the engine is likely to speed up momentarily, then
cut out abruptly when the throttle is re-opened. In
this case, first turn the mixture control screw
counter-clockwise 90
° to make sure that the
mixture has become richer, then make
incremental adjustments, each way, until an
acceptable balance between rich v.lean settings is
achieved. Carry out these adjustments patiently
under actual running conditions, until the engine
responds quickly and positively to throttle
movements. Use a small screwdriver to adjust the
mixture control valve via its slotted screwhead in
the center of the outer end of the throttle rotor. WARNING :
Note :
Remember that, if the engine is operated with the
fuel/air mixture slightly too lean, it will overheat and
run unevenly or cut out. As with all engines, it is
wise to set both valves a little on the rich side of the
best rpm setting, as a safety measure. When the
best balance of mixture adjustments has been
determined and, especially as the engine becomes
fully run-in, it will probably be found that the idling
speed has increased. Readjust the throttle opening
by means of the trim lever on the transmitter, so
that the lowest idling speed, without risk of stalling
the engine, may be obtained. 10.
For safety reasons, it is advisable to stop the
engine before carrying out adjustments to the
Mixture Control Screw.
Once the correct carburettor settings have been
established, it should be unnecessary to alter
them. Such slight Needle-Valve readjustments as
may be required to compensate for variations in
atmospheric conditions will not normally affect the
other two controls. Slight readjustments may be
necessary for optimum performance if different
types of fuel, glowplugs or propellers are used.
With the optimum mixture control valve position,
light smoke is visible during high-speed running
and engine r.p.m. increase smoothly during
acceleration. 9.
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