Linda asked: > The engine is a C-85. My normal economy-cruise is > 2150-2250 RPM (red-line on mine is 2575). Is that > "partial" enough to get the Stromberg to be working, > in your view? And what the relationship is between > amount of throttle & efficacy of the Stromberg carb > is not clear to me.
Linda, Hartmut's comments are, I think, referring to the no-EGT-gauge condition. I did my leaning with a high accuracy K&S EGT, the kind that you have to turn a knob to adjust the indicator needle. The high accuracy kind has big gradations for 10° and that let me easily see small temperature changes and adjust the EGT to 10° or even maybe 5° increments. (As opposed to the cheap EGT that has temps on the dial for 800-1600 or so and barely has more than 50° or 25° marks.) The digital EGTs should also give you 10° accuracy. I found the Stromberg carb COULD be leaned properly at any flying power level. You do NOT want to lean, normally, at full power and low altitude. If you're at a high altitude airport, you can increase your safety by doing a full-power lean (on VERY, VERY clean pavement) before takeoff. I only did this at airports 5,000' and above. I would not lean for full power climb below 5,000' but above 6,000' - 7,000' leaning can measurably increase your climb. Note that, due to thin air from around 7,500' up, the engine can't go above 75% power at best, even with the throttle to the firewall. Leaning at full power is what I saw called "leaning for power" (as opposed to "leaning for economy"). My sources told me that "leaning for power" was done to 100° rich of peak. With my gauge, I found this easy to do. Leaning for cruise economy is done to 50° rich of peak, according to my source (sorry I can't remember what that source was). I easily leaned to this setting at any cruise rpm up to 2400. I've since read articles that advocated more aggressive leaning to cruise at peak or even on the lean side of peak EGT but I want a very good source before I'd do that. When Voyager flew around the world nonstop, they did lean to the lean side of peak. I think in the book they called it "Dick's lean" setting and Dick Rutan really pushed that leaning but he did it with good 4-cylinder instrumentation so he knew that he was leaning based on information from the leanest cylinder and wasn't getting detonation. My EGT was a 1-cylinder type but I'd recommend the 4-probe type so you can monitor all the cylinders for health as well as determining the leanest cylinder in each condition (it changes). With my 1-probe EGT instrument, I would not go leaner than 100° rich of peak for power or 50° rich of peak for economy because the leanest cylinder can change and I could never know that my probe was in the leanest cylinder. (Note that during the leaning process you do lean to and just past peak before pushing in to the chosen setting, but the extra lean time isn't long.) Having the mixture control didn't seem to over-complicate my flying but I was comfortable with flying the plane when I got the mixture hooked up as I had a couple of hundred hours by then. I'd urge you to look for one of the new digital 4-probe EGT gauges and get them installed and get the Stromberg's mixture control cleaned and hooked up by or during your next annual. Then you can start to explore mixture use. If anyone has better leaning temperature recommendations (and sources), better than my 100°/50° numbers, please post them. The fuel savings in cruise at altitude can be dramatic. On a cross-country flight, you might save as much as $30 per flight leg. I think it's worth it. JMHO Ed
