If the idle mixture is correct in a carbureted engine, you needn't lean. Leaning has no effect at idle, other than taking the engine to cutoff. At any power setting above idle, adjusting the mixture in the cockpit does make a difference. You cannot adjust idle mixture from the cockpit; this is a maintenance function.
Idle mixture should be adjusted any time the aircraft is moved to a new base of regular operation, that involves a change in elevation, temperature, or climate. However, most operators don't do this. The result is a need to lean agressively.
You cannot hurt the engine at or near idle by leaning. You're best to lean almost to the point of cutoff when taxiing at idle. If you're at this point and inadvetantly attempt to take off or increase power, the engine will bark at you. It will remind you that you're far too lean. This is desirable. Taking off with the power at an intermediate point is a bad thing; if you leave the mixture at an arbitrary point, you can run into engine damage and detonation issues. Either be set for takeoff, or be agressively leaned, but nothing in-between during ground operations.
Most engine manufacturers also recommend a post-flight runup to clear the engine; I've always encouraged students and pilots to do this. Typically it involves a runup to 1,700 to 2,100 rpm just prior to shut down. (You should also routinely perform idle mixture checks and a grounding check at this time).
Performing idle mixture checks will give you an indication of how far off your idle mixture is. Run the engine up just prior to shut down, lean it out, then pull it back to idle. Run the mixture to full rich for a moment and let it idle, then slowly retard the mixture. Just prior to the engine dying, you should see a slight RPM increase of about 25 rpm or less (15-25 rpm is ideal). Less of a rise indicates a lean idle mixture, and much more of a rise indicates a rich idle mixture. If you see a rise of 100 rpm or more, your idle mixture is excessively rich, and needs to be adjusted; this accounts for your fouling problems.
Again, if the idle mixture is set properly, you can taxi all day with the mixture full rich at idle, and have no problems at all. How good is your maintenance?
Idle mixture should be adjusted any time the aircraft is moved to a new base of regular operation, that involves a change in elevation, temperature, or climate. However, most operators don't do this. The result is a need to lean agressively.
You cannot hurt the engine at or near idle by leaning. You're best to lean almost to the point of cutoff when taxiing at idle. If you're at this point and inadvetantly attempt to take off or increase power, the engine will bark at you. It will remind you that you're far too lean. This is desirable. Taking off with the power at an intermediate point is a bad thing; if you leave the mixture at an arbitrary point, you can run into engine damage and detonation issues. Either be set for takeoff, or be agressively leaned, but nothing in-between during ground operations.
Most engine manufacturers also recommend a post-flight runup to clear the engine; I've always encouraged students and pilots to do this. Typically it involves a runup to 1,700 to 2,100 rpm just prior to shut down. (You should also routinely perform idle mixture checks and a grounding check at this time).
Performing idle mixture checks will give you an indication of how far off your idle mixture is. Run the engine up just prior to shut down, lean it out, then pull it back to idle. Run the mixture to full rich for a moment and let it idle, then slowly retard the mixture. Just prior to the engine dying, you should see a slight RPM increase of about 25 rpm or less (15-25 rpm is ideal). Less of a rise indicates a lean idle mixture, and much more of a rise indicates a rich idle mixture. If you see a rise of 100 rpm or more, your idle mixture is excessively rich, and needs to be adjusted; this accounts for your fouling problems.
Again, if the idle mixture is set properly, you can taxi all day with the mixture full rich at idle, and have no problems at all. How good is your maintenance?
