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)
