O.S. Engines 21VZ-M - Manual (Page 12)

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Needle
The position of the needle-valve
when starting the engine.
Close the needle-valve approx.
30˚ after running the hull for
one full tank of fuel.
Repeat this procedure several
times.
If the engine should need to be
disassembled (e.g. for cleaning or minor
parts replacement) it is advisable to return
the Needle-Valve to the original rich,
starting setting and check whether further
running-in time is required before the car is
raced again. In the event of any major
working parts(e,g, piston/cylinder liner
assembly) being replaced, the complete
running-in should be repeated.
Remember!
Warning!
Do not touch rotating parts, engine and si-
lencer when stopping the engine as they
become very hot, and contact with them
may result in a serious burn.
Throttle Trim
Throttle Stick
TO STOP THE ENGINE
Lower the throttle trim and/or throttle stick on
the transmitter.
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Run the hull (with throttle fully open) over the
longest available straight, in order to observe
the model's speed. Next return the hull to the
starting point, close the Needle-Valve 30˚
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 hull
and reopen the Needle-Valve 30˚. 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 hull does not accelerate
smoothly and rapidly, it is probable that the
idle mixture is too rich.
FINAL ADJUSTMENT
Having established the optimum Needle-
Valve setting, check the Mixture Control
Valve setting as follows.
In this case, turn the Mixture Control Valve
clockwise 10˚. 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 Mixture Control Valve
counter-clockwise 10˚.
NOTE:
Mixture Control Valve adjustment should
be made in steps of not more than 45-90˚,
carefully checking the effect,on throttle
response, of each small adjustment.