Bill, Do you have a reference for doing the mag check at 1700 RPM? I've been doing it at 2000 RPM, but I don't think it's necessary to run it up that high to get a valid mag check. Doing it at 1700 RPM sounds better, but I'd like to know it that is written in any tech document.
Thanks, Dave --- In [email protected], William R. Bayne <ercog...@...> wrote: > > > Hi Linda, > > No, it's not OK! > > I would expect a competent mechanic to be aware that the condition you > describe is not right, (apparently) never was, and actively pursue such > a problem until it is properly resolved > > If compression is good, timing and plugs are "right", and absent > induction air leaks, more of the fuel-air mixture should be ignited and > burned with dual ignition sources during the mechanically constant > power stroke of each cylinder. When one or the other mag is not > firing, combustion is less complete and power is less from the same > fuel-air mixture, resulting in a commensurate drop in RPM. > > The mag check should be done at 1700 RPM. Between dual and > single-magneto operation there should be no MORE than 150 RPM > difference, but I would prefer to see between 25-75 RPM. The > difference in RPM when operating on either single mag. should not > exceed 75 RPM, but I do not recall much variation operating on either > mag. > > An imperceptible mag drop is strongly suggestive of unresolved ignition > circuit issues. It isn't an "open circuit" or you couldn't kill the > engine with the ignition switch, but it could be intermittently "open" > (you guess when and why). This would be a very dangerous situation if > present until resolved. > > An improperly timed or malfunctioning magneto could be the culprit. > > Substandard plugs could reduce dual-mag RPM to that of single-mag > operation. > > Remember, I'm not a mechanic! > > Regards, > > William R. Bayne > .____|-(o)-|____. > (Copyright 2009) > > -- > > On Nov 18, 2009, at 00:34, Linda Abrams wrote: > > > A big Thank You to everyone who sent ideas on possible sources of the > > intermittent run-up problems. > > > > If there were any drops on the mag test at all, it was almost > > imperceptible -- maybe half a > > needle's-worth. (Is that ok? ) > > > > Linda > > N3437H (Sky Sprite) >
