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Lean for taxi! --- CFI Tip of the Month
MarcC writes "The really nice flying weather is here (well it will be shortly!). As the weather gets warmer and the air gets even thinner, it becomes even more important to lean the airplane mixture during the taxi. A full rich mixture combines the most fuel per volume of air to enter the engine cylinders. The higher the density altitude, the leaner the mixture needs to be for proper engine operation.While we should all follow our POH's for leaning procedures, it makes sense to lean out the mixture after engine start and before takeoff. Too much fuel in the cylinder at lower power settings can cause spark plug fouling which is a buildup of deposits on the spark plug electrode. It shows up as a significant drop in RPM while doing a magneto check. This generally isn't a problem at higher power settings which is why we should usually be at full rich (near sea level) for takeoff.
Properly clearing a fouled plug requires a slightly higher power setting and a leaner mixture. Take caution not to lean out too much at high power as that can cause excessively high engine temperatures. It's an awful feeling to get to the hold short line on a beautiful day and have magneto problems. That extra step on the checklist "Lean for taxi" can get you in the air a lot faster!"
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