Piper Arrow IV, Maintenance Manual

Page: 607 / 752

ADJUSTMENT OF IDLE SPEED AND MIXTURE.
1. Start the engine and warm up in the usual manner until oil and cylinder head temperatures are normal.
2. Check magnetos. If the “mag-drop” is normal, proceed with idle adjustment.
3. Set throttle stop screw so that the engine idles at 550-600 RPM. If the RPM changes appreciable after
making the mixture adjustment during the succeeding steps, readjust the idle speed to the desired RPM.
4. When the idling speed has been stabilized, move the cockpit mixture control lever with a smooth,
steady pull toward the “Idle Cut-Off” position and observe the tachometer for any change during the leaning
process. Caution must be exercised to return the mixture control to the “Full Rich” position before the RPM
can drop to a point where the engine cuts out. An increase of more than 10 RPM while “leaning out” indicates
an excessively rich idle mixture. An immediate decrease in RPM (if not preceded by a momentary increase)
indicates the idle mixture is too lean.
5. If the above indicates that the idle adjustment is too rich or too lean, turn the idle mixture adjustment
in the direction required for correction, and check this new position by repeating the above procedure. Make
additional adjustments as necessary until a check results in a momentary pick-up of approximately 5 (never
more than l0) RPM. Each time the adjustment is changed, the engine should be run up to 2000 RPM to clear
the engine before proceeding with the RPM check. Make final adjustment of the idle speed adjustment to
obtain the desired idling RPM with closed throttle. The above method aims at a setting that will obtain
maximum RPM with minimum manifold pressure. In case the setting does not remain stable, check the idle
linkage; any looseness in this linkage would cause erratic idling. In all cases, allowance should be made for the
effect of weather conditions and field altitude upon idling adjustment.
CONTROLLING.
ADJUSTMENT OF THROTTLE AND MIXTURE CONTROLS. (Refer to Figure 73-10.)
Throttle and mixture controls are adjusted so that when the throttle arm on the fuel injector is rotated
forward against its full throttle stop and the mixture control is rotated forward against its full rich stop, the
cockpit control levers of the throttle and mixture should have 0.010 to 0.030 of an inch spring back on
instrument panel stop when in full throttle or full rich position.
1. The throttle may be adjusted as follows:
A. At the fuel injector, disconnect the clevis end of the throttle control cable from the control arm.
Loosen the jam nut that secures the clevis end.
B. Adjust the linkage by rotating the clevis end on the cable to obtain 0.010 to 0.030 of an inch spring
back on instrument panel stop when in full throttle position.
C. On aircraft equipped with air conditioning systems, a micro switch is located below the throttle
control which is set to actuate in the full open position. With the throttle control adjusted to obtain
a clearance of .010 to .030, adjust the micro switch to actuate at this point also.
D. Reconnect the clevis end to the control arm and safety.
Effectivity 73-20-01
PA-28RT-201 Page 73-14
December 1, 1978
3D3
PIPER AIRCRAFT
PA-28RT-201 / 201T
MAINTENANCE MANUAL