28
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 be accompanied by visibly
diminished exhaust smoke and the model will lose
speed. At this point, throttle down immediately, stop
the vehicle and reopen the Needle-Valve 15˚.
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 or Mixture
Control Screw 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 or
Mixture Control Screw counter-clockwise 15˚.
Adjust high RPM running.
Adjust medium and low RPM running.
Carry out adjustment by 15
degrees at a time for both
closing and opening.
29
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 or Mixture
Control Screw 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 maximum
performance.
NOTE
The above mentioned needle opening is a guide. It
varies according to the fuel used and silencer.
Usually, when a lower nitro content fuel used, it will
be necessary to close the needle-valve.
Do not close the needle-valve too much or rust will
be generated and the engine will be damaged.
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.
