O.S. Engines 21VZ-B V-Spec - Manual (Page 22)

With the engine running, close the throttle
and allow it to idle for about five seconds,
then reopen the throttle fully. If, at this point,
the engine puffs out an excessive amount of
smoke and the vehicle does not accelerate
smoothly and rapidly, it is probable that the
idling mixture is too rich. In this case, turn
the Metering Needle clockwise 45-90°. If, on
the other hand, the engine tends to speed up
momentarily and then cut out abruptly when
the throttle is opened, the idling mixture is
too lean. Correct this by turning the Metering
Needle counter-clockwise 45-90°.
NOTE:
Metering Needle adjustment should be
made in steps of not more than 45-90°,
carefully checking the effect.on throttle
response, of each small adjustment.
Carry out adjustments patiently, under actual
running conditions, until the engine responds
quickly and positively to the throttle control.
Warning!
Mixture adjustments (whether via the
Metering Needle, 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 the needle-valve and
metering needle 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.
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