Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 670 / 881

7. Check the adjustment of the idle mixture and idle speed.
ADJUSTMENT OF IDLE MIXTURE. (Refer to Figure 73-1.)
— WARNING —
WHEN PERORMING ENGINE WARM-UP INDOORS, PROVIDE A BARRIER
ABOUT THE ENGINE TO PREVENT SERIOUS INJURY. ALSO PROVIDE
ADEQUATE MEANS OF VENTILATING THE WORK AREA.
1. After performing the standard engine starting procedure, operate the engine for at least two minutes between
800 to 1200 RPM to insure proper engine warm-up.
2. Position the cockpit throttle control lever to obtain a reading of approximately 550 RPM on the tachometer
with the idle mixture control at the full rich position.
3. While observing the tachometer, slowly pull the mixture control towards the idle cut-off position. The
optimum mixture is obtained when the RPM increases slightly (10 to 50 RPM) prior to engine speed
decreasing.
4. Following the momentary increase in RPM, the engine speed will start to drop. Immediately move the
mixture control to the full rich position to prevent the engine from cutting out completely.
5. Should these steps reveal that the idle mixture is not correct make the following adjustments and perform
Steps 2 thru 4 again.
A.
With the engine set to idle at 550 RPM turn the idle mixture adjusting screw at the rear of the
c a r b u r e t o r, clockwise, leaning the fuel mixture. Continue to do this until the engine begins to run
roughly, at which time the engine speed will decrease.
B. Turn the adjustment screw counterclockwise until the engine runs smoothly again. Continue to turn
the screw in the same direction until the engine begins to run roughly once more. At this point, the
fuel mixture will be too rich and engine speed will decrease again.
C. Now adjust the screw to a midway position between the lean and rich fuel mixture; the RPM of the
engine will reach a minimum speed for idle mixture settings.
6. After adjusting the idle mixture, recheck it several times to insure its remaining consistent from high power
settings back to idle.
ADJUSTMENT OF IDLE SPEED. (Refer to Figure 73-1.)
1. Pull back the cockpit throttle control lever until it is completely aft and in the closed position. Observe the
engine speed on the tachometer.
2. Adjust the idle speed adjustment screw to obtain from 550 to 650 RPM. Rotate the screw clockwise to
increase the speed of the engine; counterclockwise to decrease the engine speed. The screw is located on
the throttle arm.
— Note —
One complete revolution of the carburetor idle screw provides a variation of
approximately 100 RPM in idling speed.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
7 3 - 11 - 0 2
Page 73-02
Revised: May 15, 1989
3F4
PIPER AIRCRAFT