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17. WARMING UP THE ENGINE
As a carburetor type, the engine sometimes hesitates, stalls, and has unstable idling when Cylinder Head
Temperature (CHT) is low, below 100
℃
. So warming up is needed when CHT is low by increasing the rpm
of idling (700 – 800 more than usual) and refraining from moving the throttle stick quickly. In case you
need quick warming up, increase the rpm of idling up to 3,000 – 4,000rpm, so that CHT raises more than
100
℃
within several tens of seconds.
18. THE ADJUSTMENT OF CARBURETOR
(1) The range of adjustment by the slow needle and the high needle
Fig 7
Fig.7 shows the adjustment ranges. The slow needle affects even full throttle range and the high needle
affects 1/4 throttle opening. The slow needle and the high needle affect each other in a wide range
generally for gasoline engine carburetors, so both needles need to be adjusted in the range of hovering.
(2) Adjustment during taking off
When the engine is started and has stable idling, move up the throttle stick gradually for taking off.
①In case the engine “stutters” or “coughs” and hesitates to increase rpm without much power, the slow
needle is too rich. Turn in /clockwise the needle by 15 degrees and try taking off. Repeat the
procedure until you can take off the aircraft.
②In case rpm does not increase with sluggish acceleration, and the engine dies quickly, the fuel mixture is
lean. Turn the slow needle out/counter-clockwise by to richen the fuel mixture.
(3) Adjustment during hovering
Count the rpm of main rotor during hovering.
①In case the rpm of main rotor is higher than you desire, set the throttle curve lower and turn the slow
needle out/counter-clockwise by 30 degrees to richen the fuel mixture.
②In case the rpm of main rotor is lower than you desire and you lose altitude of the hovering aircraft,
probably the slow needle is set rich. Turn the slow needle out/counter-clockwise by 15 degrees to lean the
fuel mixture.
(4) Adjustment in flight
Basic engine adjustment during actual flight after breaking in
① Turn out/counter-clockwise the high needle by 30 degrees from the factory setting to check if it affects
hovering.
② Change the hovering mode to flight mode to fly around and check the engine performance in flight.
Losing power at full throttle, engine stall, over rev at lower rotor pitch are symptoms of lean needle
adjustment. When the needle adjustment is lean, the engine loses power and stalls abruptly. Start from
rich adjustment and lean the adjustment gradually.
③The engine gets overloaded and overheats even the slow and high needles are adjusted a little rich when
the main rotor maximum pitch is too high. Also, the engine overheats when it over-revved at low rotor pitch.
Summary of Contents for GT120THU
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