O.S. Engines 12TZ(P) - Manual (Page 11)

20
FINAL ADJUSTMENT
Throttle
Stop Screw
Needle Valve
Metering
Needle
Open Close Close Open
Needle Valve Metering Needle
More fuel Less fuel More fuel Less fuel
Run the vehicle (with throttle fully open) over
the longest available straight course, in order
to observe the model's speed. Next return
the car to the starting point, close the Needle-
Valve 15˚ and repeat the run, taking note of
the improvement in performance.
Continue with further runs, gradually
reducing the Needle-Valve setting and
aiming to achieve the highest straight-line
speed. Remember, however, that, if the
Needle-Valve is shut down too far, the
engine will overheat and, accompanied by
visibly diminished exhaust smoke, the model
will lose speed. At this point, throttle down
immediately, stop the vehicle and reopen the
Needle-Valve 15˚.
Final adjustment should be carried out only after
the running-in has been completed.
21
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 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
idle mixture is too rich.
Carry out adjustments patiently, under actual
running conditions, until the engine responds
quickly and positively to the throttle control.
In this case, turn the Metering Needle
clockwise 15˚. If, on the other hand, the
engine tends to speed up momentarily and
then cut out abruptly when the throttle is
opened, the idle mixture is too lean. Correct
this by turning the Metering Needle
counter-clockwise 15˚.