GRUMMAN AMERICAN
FOR TRAINING USE ONLY – SECTION 4
MODEL GA-7/COUGAR
NORMAL PROCEDURES
4-20
Issued: April 10, 1978
NOTE
On new engines, power should be maintained at 75 percent power or more until
a total of 50 hours has accumulated. This is to ensure proper seating of the rings
and is applicable to new engines, engines in service following cylinder
replacement, or top overhaul of one or more cylinders.
MIXTURE LEANING PROCEDURES
Fuel consumption can be reduced significantly and engine performance improved, especially at high altitudes, by
leaning the mixture. The leaning procedure may be monitored by the exhaust gas temperature (EGT) indicator (if
installed) or by the engine performance. Never lean the mixture to the point that the maximum (red line) cylinder
head temperature is exceeded.
LEANING WITHOUT EGT (EXHAUST GAS TEMPERATURE) SYSTEM
During climb, roughness or loss of power may result from over-richness. In this case, lean the mixture only enough
to obtain smooth engine operation, not for economy. Monitor engine instruments for temperature rise. Rough
engine operation due to over-rich fuel/air mixture is most likely to be encountered at altitudes above 5000 feet.
For flight with one engine inoperative, the mixture should be leaned to best power.
BEST POWER
For best engine power, lean the mixture as follows:
1.
Slowly move the mixture control from the FULL RICH position toward the LEAN position.
2.
Continue leaning until engine roughness is noted.
3.
Move mixture control forward approximately 1/2 inch toward the FULL RICH position.
BEST ECONOMY
For optimum fuel consumption at 75% power or less during cruise, lean the mixture and observe engine
performance as follows:
1.
Slowly move the mixture control from the FULL RICH position toward the LEAN position.
2.
Continue leaning until engine roughness is noted.
3.
Enrich the mixture slightly until the engine runs smoothly.
The mixture should be adjusted on one engine at a time. Always return the mixture to FULL RICH before increasing
the power settings.
In order to maintain smooth engine operation, it may be necessary to enrich the mixture slightly during the
descent.
LEANING WITH EGT (EXHAUST GAS TEMPERATURE) SYSTEM
The exhaust gas temperature (EGT) indicator is offered as an optional item on the GA-7/Cougar. The EGT can be
used to optimize the mixture setting and reduce the fuel flow. This normally results in more consistent aircraft
performance. The following mixture settings are normally used when using the EGT for a reference.
1.
FULL RICH mixture.
2.
Best Power – 100°F on the rich side of peak EGT.
3.
Best Economy – Operate at peak EGT.