O.S. Engines 91HZ-R 3C - Manual (Page 20)

38
CARBURETOR CLEANLINESS
Remove this with
an 8mm wrench
Dirt and fibrous matter
mostly accumulate here
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.
It is recommended that fuel is passed through a
filter when the tank is filled and that a good in-line
filter is installed between the fuel tank and
carburetor and, furthermore, that this filter is
frequently cleaned to remove foreign matter that
accumulates on the filter screen.
Finally, occasionally remove the needle-valve
holder from the carburetor as shown in Picture and
extract any remaining foreign matter that may have
lodged in the location shown in Picture, right.
39
ADJUSTING CHART
High Speed Needle Valve - two and half turns open from fully closed position. Medium Speed Needle Valve - one turn open from fully closed position.
Start the engine
Warm up the engine
Observe the mixture condition while "floating" the model
Turn the Idle Mixture Control
Screw
counter-
clockwise 5 degrees
Idling OK
Turn the Idle Mixture Control Screw clockwise 5 degrees
Lean mixture
Rich mixture
Observe the hovering mixture condition
Open the High Speed Needle Valve (Turn counter-clockwise)
Hovering OK
Lean mixture
Rich mixture
Close the High Speed Needle Valve (Turn clockwise)
Land the model
Idle for approx: 10 seconds, then reopen throttle to observe transition ("Float" the model)
Idling OK
Lean mixture
Rich mixture
High Speed Flight
Lean mixture
Rich mixture
High Speed Flight OK
Fine tuning of hovering mixture
Open the Medium Speed Needle Valve
Hovering OK
Adjustment completed
Open the High Speed Needle Valve (Turn counter-clockwise)
Close the High Speed Needle Valve (Turn clockwise)
Fine tuning of idling mixture
Lean mixture
Rich mixture
Idling OK
Lean mixture
Rich mixture
Close the Medium Speed Needle Valve Turn the Idle Mixture Control Screw clockwise 5 degrees Turn the Idle Mixture Control Screw clockwise 5 degrees
Turn the Idle Mixture Control
Screw
counter-
clockwise 5 degrees Turn the Idle Mixture Control
Screw
counter-
clockwise 5 degrees