Adjustment Of Throttle And Mixture Controls; Adjustment Of Idle Speed And Mixture; Removal Of Fuel-Air Bleed Nozzle; Cleaning And Inspection Of Fuel-Air Bleed Nozzle - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
8-64. ADJUSTMENT OF THROTTLE AND MIXTURE CONTROLS. The throttle and mixture controls
are adjusted so that when the throttle arm on the injector is rotated forward against its full throttle stop
and the mixture arm is rotated forward against its full rich stop, their respective cockpit control levers
should be .062 to .125 inch in from their full forward stops, which are located in the control pedestal.
a. At the injector, disconnect the throttle and/or mixture control cable end from its control arm.
b. Loosen the jam nut securing the cable end.
c. Adjust the linkage by rotating the cable end to obtain the .062 to .125 inch spring back of the
cockpit control lever when the throttle or mixture control arm contacts its stop.
d. Reconnect the cable end to its control arm and secure jam nut.
e. Pull the throttle and mixture control lever in the cockpit full aft to ascertain that the injector idle
screw contacts its stop and the mixture control arm contacts its lean position.
8-65. ADJUSTMENT OF IDLE SPEED AND MIXTURE.
a. Start the engine and warm up in the usual manner until oil and cylinder head temperatures are
normal.
b. Check magnetos. If the "mag-drop" is normal, proceed with idle adjustment.
c. Close the throttle to idle. If the RPM changes appreciably after making the idle mixture
adjustment during the succeeding steps, readjust the idle speed to the desired RPM.
NOTE
The idle mixture must be adjusted with the fuel boost pump
"ON."
d.
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 50 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.
e. 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. 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.
8-66. FUEL AIR BLEED NOZZLE.
8-67. REMOVAL OF FUEL-AIR BLEED NOZZLE. The nozzles must be carefully removed as they orthe
cylinders may be damaged.
a. Remove the lower engine cowl. (Refer to paragraph 8-6.)
b. Disconnect the fuel line from the nozzle.
c. Remove the spring retainer and spring from the nozzle stem.
d. Disconnect the nozzle shroud from the vent hose and remove it from the nozzle.
e. Carefully remove the nozzle, using the correct size deep socket.
8-68. CLEANING AND INSPECTION OF FUEL-AIR BLEED NOZZLE.
Reissued: 9/23/80
POWER PLANT
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