22
Warning!
Carry out adjustments patiently, under
actual running conditions, until the engine
responds quickly and positively to the
throttle control.
Mixture adjustments (whether via the
Mixture Control Valve, or the Needle-Valve)
cannot be made accurately under 'no-load'
conditions, which, in any case, are not
advised, since such operation carries the
risk of seriously damaging the engine
through over-revving and overheating.
With the optimum mixture control position,
light smoke is visible during high speed
running,and the engine rpm increases
smoothly during acceleration. Remember
that, if the engine is operated with the fuel/air
mixture slightly too lean, it will overheat and
run unevenly. As with all engines, it is
advisable to set both needle-valve and
mixture control screw very slightly on the rich
side of the best rpm setting, as a safety
measure.
If the engine runs too fast with the throttle
closed, the throttle stop screw should be
turned counter-clockwise to allow the throttle
opening to be reduced.
Finally, beyond the nominal break-in period,
a slight readjustment toward a leaner needle
setting may be required to maintain
performance.
23
REALIGNMENT OF MIXTURE CONTROL VALVE
In the course of making carburetor
adjustments, it is just possible that the
Mixture Control Valve may be inadvertently
screwed in or out too far and thereby moved
beyond its effective adjustment range.
Its basic position can be found by first rotating
the Mixture Control Valve until its slotted head
is flush with the carburetor body.
The valve is then screwed in exactly 0.5 turns
to re-establish its neutral position.
Carburetor Body
Mixture Control Screw
First rotate the Mixture Control
Screw until its slotted head is
flush with the carburetor body.
Then screw the valve in
exactly 0.5 turn.
This is the standard position.
Throttle Lever
CARBURETOR CLEANLINESS
The correct functioning of the carburetor depends on its small fuel orifices remaining clear.
NOTE:
It is necessary to readjust the needle-valve
when the plug, propeller, fuel, silencer, etc.
are changed. Also, needle setting varies to
atmospheric conditions (temperature,
humidity, pressure) even in the same day.
Readjust the needle if necessary watching
the engine running conditions.
