Piper COMANCHE PA-24-180 Service Manual page 317

PIPER COMANCHE SERVICE MANUAL
d.
When the idling speed has been stabilized. move the cockpit mixture control 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 excessiely 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 abo\e
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
7-38. Ignition System.
7-39. Magneto.
CAUTION
Ascertain that the primar! circuits of both magnetos are grounded
before working on the engine
7-40 Inspection Of Magnetos. At time of engine inspection or when a magneto has been removed from
the engine. the following checks may be performed. Each step in the check list is keyed by number to a
pan shown in Figure 7-8
a
Inspect distributor block contact springs If broken or corroded. they should be replaced
b
Inspect oil felt washer. It should be saturated with oil. If dry. check for worn bushing Of K .add
No. 30 oil
c
Inspect distributor block for cracks or burned areas The wax coating on the block should not be
remo\ed Do not use solvents
d.
Look for excess oil in breaker compartment If present. it may mean a bad oil seal or oil seal
bushing at drive end Check manufacturer's overhaul procedure
e.
Look for frayed insulation or broken wire strands in leads in back of magneto. See that terminals
are secure Be sure wires are properlN positioned The position of the leads in the 200 series breaker
compartment must be as shown in Figure 7-9. otherwise chafing or breaking may result
f
Inspect capacitor visually. If possible test for leakage. capacity and series resistance Remember. an
electrical failure of an aircraft capacitor is rare
g.
Adjustment of breakers must be correct for proper internal timing of magneto (Refer to
paragraph 7-42 )
h
Check if breaker cam is clean and smooth. if cam screw is tight (25 in lbs ) If new points are
installed. blot a little oil on cam
ISSUED: 8/18/72
2B7
POWER PLANT
2B7