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Answer: The most logical initial action is to " Check the result obtained with a leaner setting of the mixture". Option A is most correct.
Explanation: in a carburetor engines, roughness of the engine is always caused by the mixture of air and fuel differences in the cylinders. When this is noticed during elevation. The first thing a pilot need to do first is to check the mixture of air and gas applied to the leaning settings. Then enrich the mixture of air and fuel gently, this is done by reducing the density of air, until the engine start running smoothly.
If the mixture of air and fuel is over leaned the RPM will begin to drop, which will lead to roughness in the engine
