Carburetor Controls Adjustment; Idle Speed And Mixture Adjustment (Carburetor) - Piper PA-24 Comanche Service Manual

PIPER COMANCHE SERVICE MANt:AL
7A-51. Adjustment Of Carburetor Controls. (Refer to Figure 7-6a.) The throttle mixture and carbure.
heat controls are adjust.ed so that ,;,'hen the throttle arm ?n
t~e
carbu:retor is rotated forward against
it'>
throttle stop and th.. mixture arm
IS
rotated forward against Its full rich stop and the carburetor heat arm is
rotated to the full ram air position. their respective cockpit controls should be .062 of an inch OUt from
their full forward stops,
a. Disconnect throttle control cable at the carburetor and loosen the jam nut securing the cable end.
b. Adjust the linkage by rotating: the cable end to obtain the .062 of an inch spring back
01
the
cockpit control when the throttle arm contacts it stop.
c. Reconnect the cable end to the control arm and secure jam nut.
d. Adjust mixture and carburetor heat control by loosening the castelled nut at the control arms and
sliding control cable through the stud until the .062 of an inch spring back of the cockpit control
is
obtained
when the mixture is in the full rich position and the carburetor heat is in the full ram air position.
e. Tighten caste lied nut and safety.
f.
Pull the throttle. mixture and carburetor heat controls in the cockpit full aft to ascertain that the
throttle arm contacts the idle screw and the mixture control arm contacts its idle cut-off stop and the
carburetor heat flap valve is in the full carburetor heat position.
7A·5"}', Adjustment Of Idle Speed And Mixture. (Carburetor)
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.
;\;OTE
The idle mixture must be adjusted with the fuel boost pump ··O~".
•
d. When the idling speed has been stabilized. move the cockpit mixture control with a smooth. steady
pull toward the "Idle Cut·OW· 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
R PM 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 adjust rnent.
ISSt'ED: 8/18/72
2D12
POWER PL.-\.