I have to agree with the other BB. No mag drop is bad. Could be sign of a bad p-lead or mis timing.
Some mechanics will intentionally mis-time the mags to get less mag drop. This risks loss of power at maximum RPM. do your normal mag check at whatever high RPM you choose, after the check -right, check-left, at high RPM turn to OFF. DO NOT TURN BACK ON TIL ENGINE IS COMPLETELY STOPPED!!!! it could backfire and blow your muffler apart If engine does not stop it is a bad p-lead, switch or open in the grounding circuit. Could be intermittent If engine doesn't stop, pull power to idle and turn fuel off. Bill CC: [email protected] To: [email protected] From: [email protected] Date: Wed, 18 Nov 2009 12:36:25 -0600 Subject: Re: [ercoupe-tech] intermittent run-up problems solved I think I disagree that it's not ok. Linda said she has a barely perceptible drop (which is what I get with my C-90 in a 415C). But then you say 25 to 75 is ok and your preference. In my mind a 25 rpm drop is "barely perceptible" and about a half needle width. Dan Caliendo Ercoupe Mach 0.14 3658H On Nov 18, 2009, at 4:00 AM, William R. Bayne 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) _________________________________________________________________ Windows 7: I wanted simpler, now it's simpler. I'm a rock star. http://www.microsoft.com/Windows/windows-7/default.aspx?h=myidea?ocid=PID24727::T:WLMTAGL:ON:WL:en-US:WWL_WIN_myidea:112009
