Subscriber question:
"I’ve read about leaning on taxi to save fuel, but my instructor says it’s not worth the risk of a lean takeoff unless you have a serious plug fouling problem. What do you think?" — Amelia B.
Tom:
“If saving fuel hasn’t convinced you to lean the engine while taxiing, have you considered the environmental impact of emitting more lead into the atmosphere than you need to?
Recent reports suggest leaning while taxiing can reduce lead emissions on the ground by at least 20 percent, and considering that GA flying is under high scrutiny by environmental groups and some municipalities, we should do all we can to fly in a friendly way. Because of lead emissions, two airports in southern California have eliminated the availability of 100LL and others are now looking into doing the same thing. So, consider pulling the red knob way back right after start up.
A Continental IO-550, for example, at about 1000 RPM, burns about six gallons per hour. Pulling the mixture back to about three gallons per hour reduces lead emissions significantly. And, of course, on a 10-minute taxi out you’ll also save nearly half a gallon of fuel. With the national average price of 100LL at $6.19 (and many places much more than that), you can pocket about three bucks—and save on future maintenance through reduced spark plug fouling and by having a cleaner engine.
Remember though, to pull the mixture back to the point that the engine will stumble if you try to apply full power for takeoff without richening the mixture again. Tell your instructor that taxiing while that lean will not hurt the engine, and that you want to save money as well as reduce your environmental impact.
Lean and be green, while we all look forward to the availability of a high-octane unleaded fuel for the entire GA fleet.”