REFLECTOR: Franklin Mag

[John Dibble]

Ronnie,

Thanks.  That helps a lot.  I had used a flashlight to set the timing.  The light dims
a little when the points open.  But it just isn't running right on the mag.  An
observer commented that it sounded like it was too advanced.  The mag was snapping at
the advance mark, and from what you just wrote, that confirms that it is too
advanced.  Also at 1200 rpm it runs rough on just the mag.  At 1500 rpm, when I switch
off the mag the rpms drop as expected.  When I switch off the EI, the rpm stays about
the same as when both are on.  I think this is also indicating that it is too
advanced.
Tomorrow I am going to make some more adjustments.  I can tell from how it runs when
it's right, I just wanted to confirm that it is too advanced.

John

Ron Brown wrote:

> Hi John,
>
> On a Lycoming, the impulse coupling snaps at Top Dead Center.
>
> The timing should be set on the advance mark, after the mag snaps.  IE, turn
> the engine over until it snaps on Cylinder number 1, then turn the engine
> backwards about 45 degrees.  Then go forward again and set the timing at the
> advanced mark - on my 200 hp angle valve Lycoming IO 360 this is 25 degrees
> Before Top Dead Center (or 22 according to a service bulletin or 20 degrees
> for higher compression pistons).  Sorry, I don't know what the timing for a
> Franklin is supposed to be.
>
> You'll need a buzz box or a sensitive digital ohmmeter to sense the opening
> of the points.  The resistance will change from about 0.5 ohms to about 0.7
> ohms when the points open. (and don't let the mag snap while the ohmmeter is
> connected - it may zap the ohmmeter).
>
> Oh and a bit of explanation - the spark during starting needs to be retarded
> or else the engine will kick back (some times so severe that it can break
> the starter or starter gear).  So the impulse coupling delays the spark
> until TDC while the engine is being turned slowly by the starter. Then when
> the impulse coupling snaps (releases), it causes the magneto to spin faster
> thereby
> generating a hotter spark for cranking.
>
> That is one thing to look for when the engine doesn't seem to want to
> crank - if you don't have the impulse coupling snapping, the spark is weak
> and the engine will be difficult to start.
>
> Ronnie
>
> ----- Original Message -----
> From: "John Dibble" <aminetech at bluefrog.com>
> To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
> Sent: Thursday, November 16, 2006 6:37 PM
> Subject: Re: REFLECTOR: Franklin Mag
>
> > I'm trying to set the timing on the mag.  When turning the prop by hand,
> > does the mag
> > snap at the advance timing mark, or at another spot?
> >
> > John
> >
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