O.S. Engines 55AX - Manual (Page 18)

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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.
34
1
2
3
Symptom Factor Cause Corrective action
Recharge the electric starter battery.
Recharge lead-acid cell or replace dry battery. (Note: An unused, or almost
unused, dry battery may sometimes be of insufficient capacity if it is "old
stock".)
Replace glowplug. Check that applied voltage is not too high.
Check glowplug heating using other leads.
Close needle-valve fully and remove glowplug, then flip propeller to pump
out excess fuel. (Invert engine, if possible, while pumping out excess). Re-
start engine. (Priming is not necessary at this time.)
Repeat priming procedure referring to Priming.
Sluggish rotation
Glowplug battery
discharged.
Glowplug element is
burned out
Something wrong with
battery leads.
Engine "flooded" due to
excessive priming.
Insufficient priming.
Engine fails
to fire.
. . . . . .
. . . . . .
. . . . .
. . . .
. . . .
. . . . .
TROUBLE SHOOTING WHEN THE ENGINE FAILS TO START
Four key points
For quick, reliable starting, the following four conditions are required.
1 Good compression. 2 Adequate "glow" at glowplug. 3 Correct mixture.
4 Sufficient electric starter rotating speed.
If the engine fails to start, or does not keep running after being started, check symptoms against the
following chart and take necessary corrective action.
Note: The most common causes of trouble are marked with three asterisks, the less common problems
with one or two asterisks.