We have a problem with the Continental 90 in the M-10, and I wanted to see if any of you have seen this before. The symptoms are:
* Excessive RPM drop on only one mag (either one). About 200 RPM, with occasional backfiring in 1600-2000 RPM range. * Mag drops at 1500 RPM or below are only 25-50 RPM. * Engine has trouble taking power above 1500 RPM, but above 2000 or so, it seems to have no problem. * In this "bad" rpm range from about 1600-2000, leaning does not cause a rise, but a drop as the control reaches about halfway out. * Engine reaches full-power, with full RPM, and the mag drop there is only 50 RPM or so. >From all of this I'm assuming that (probably) the carb is running lean in this range. Here are the "knowns": * It has always had this symptom to some extent, but was usually attributed to fouled plugs and what-not. Lately it has gradually become more pronounced. * The carb was just overhauled by yours truly, with the supervision of an IA. No obvious problems were found. Float levels are correct, and fuel flow and pressure to the carb is fine. We did it by the book. * The carb is an MA-3 with the single-piece venturi added per AD, before we got the plane. It has no "economizer" jet. * All cylinders are new Milleniums. They don't have any obvious problems, except that they all have oil in them. The AI attributes this to the fact that the rings haven't fully seated yet. They have about 3 hours on them. This rough-running condition existed before the cylinders were replaced, but not to this extent. * The engine has new Slick mags, and the timing has been checked and rechecked. Again, this problem was there before the mag change. New harness and plugs too. Those are the facts. Anybody have any experiences like this? I don't think it's a fuel-flow problem, because full power seems OK. The AI says he thinks he remembers something about the one-piece venturi causing mixture problems in some cases. Anybody heard this one?
<<attachment: winmail.dat>>
