24
RUNNING-IN ("Breaking-in")
For running-in, fit the engine with a well-
balanced propeller intended for actual flight.
Use a fuel mixture as specified. Running-in
procedure is the same as for a conventional
reciprocating model engine. After starting the
motor, open the throttle fully, but use a rich
needle-valve setting to reduce rpm, increase
lubrication and lower running temperature. This
will produce a smoky exhaust but will ensure
that the engine does not become overheated
and damaged during this critical period.
Install the engine with the propeller intended
for your model. Run the engine for one min-
ute with the throttle fully open, but with the
needle-valve adjusted for rich, slow “four-
cycle” operation. Then, adjust the needle-
valve so that the engine just breaks into
“two-cycle” from “four-cycle” operation, and
run the engine for 2 tanks. (Even when the
exhaust note is not clear, if the r.p.m. lower,
the needle-valve is closed a little too much.)
Fly the model with rich needle-valve setting.
The needle-valve can be gradually closed
after each flight to give more power. How-
ever, if the engine shows sings of running
too lean, the next flight should be set rich.
Avoid successive “nose-up” flights.
After a total of ten flights, the engine should
run continuously, on its optimum needle-
valve setting, without loss of power as it
warms up.
1.
2.
3.
25
SUBSEQUENT READJUSTMENT
Once the engine has been run-in and the
controls properly set up, it should be
unnecessary to alter the mixture settings;
except to make minor adjustments to the
Needle-Valve occasionally, to take account of
variations in climatic conditions. The use of a
different fuel, however, particularly one
containing more, or less, nitromethane and/or
a different type or proportion of lubricating oil,
is likely to call for some readjustment of the
Needle-Valve. Remember that, as a safety
measure, it is advisable to increase the
Needle-Valve opening by an extra half-turn
counter-clockwise, prior to establishing a new
setting. The same applies if the silencer type is
changed. A different silencer may alter the
exhaust pressure applied to the fuel feed and
call for a revised Needle-Valve setting. The
use of a different glowplug may also require
compensating carburetor readjustments.
CARBURETOR CLEANLINESS
The correct functioning of the carburetor
depends on its small fuel orifices remaining
clear. The minute particles of foreign matter
that are present in any fuel, can easily partially
obstruct these orifices and upset mixture
strength so that engine performance becomes
erratic and unreliable.
O.S.'Super-Filters'(large and small) are
available, as optional extras, to deal with this
problem. One of these filters, installed on the
outlet tube inside your refueling container, will
prevent the entry of foreign material into the
fuel tank. It is also recommended that a good
in-line filter be installed between the tank and
needle-valve. Do not forget to clean the filters
regularly to remove dirt and lint that
accumulate on the filter screen.
Also, clean the carburetor itself occasionally.
