John: I'm curious enough to read that SB on the Continental IO-550 fuel system. Perhaps others would also like to read it if you post the file to wherever marv saves files like that. Or a link to an outside source. I'm even more curious why so many Lancair pilots tolerate a engine/fuel system that is clearly finicky. Even Joe B reported that he has had surging on takeoff that was cured by flipping a switch. A reliable system is one that stays within its proper operating range even when its inputs are out of spec. It appears from the published accounts on this forum that the fuel flow varies with fuel supply pressure. Q: Why does the engine care which fuel pumps are on? A: Because the fuel flow varies with fuel pressure.
Q: Why does the fuel flow depend on pressure? A: Because it is not regulated. Q: Why is the pressure not regulated? A: Because Continental customers are willing to do the job by hand. It seems that the job of fuel flow regulation is relegated to the pilot. The pilot has access to two pump switches, a mixture knob, and a fuel cutoff valve. With those tools he attempts to keep the fuel flow to the cylinders within a narrow range of acceptable mixtures. If he fails, the engine quits now, or overheats, detonates, and may quit later. Admittedly, most Lancair pilots are quite a bit smarter than a pressure regulator or a float bowl, but they also require more recurrent training, and are easily distracted. It appears to me that the safety of these pilots and their
passengers could be improved more by fixing the flaws in the fuel supply and injection system than by learning better switchology. Jeff asked if I have taken my Toyota to FL260... No, I have never taken my Toyota to FL260, nor to -60F. My expectation is that it will work fine at -60F, but probably not at FL260 on 87 octane auto gas. It is not an exact comparison, but I hope it provides some food for thought. 175,000 miles is approximately 4000 and 5000 operating hours. The spark plugs were replaced once. It runs smoothly from 800 to 7000 RPM. The fuel mixture has NEVER been adjusted except by the built-in fuel regulation mechanisms. The fuel itself changes seasonally. The temperature has ranged from -40F to 120F. I would say the Toyota fuel injection system is better
engineered to meet its expected operating conditions than the system in the Continental. The same could be said for the Marvel Schebler MA4-SPA carburetor in my Lancair, though it needs much more maintenance and in-flight twiddling than the Toyota. 'nuff said. -bob
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