F-20 Magneto Mysteries? for Nebraska Kirk, Jan Nicholson

erskine2017 · Jul 11, 2017

If the F-20 Magneto impulse snaps at TDC with the advance lever retarded, what will the running timing be with the lever still retarded. The impulse must retard the timing somewhat. Surely there must be a lag angle independent of the advance lever. Please explain.

Janicholson · Jul 11, 2017

I believe it is minimal, maybe 4 or 5 degrees. The impulse needs time to accelerate the magnet to make cranking speed spark. Put several marks ahead of tdc at about an eighth of an inch apart. Use a timing light on it. to see where the timing sparks when the impulse is clicking. then start it and look at the marks. Calculate the circumference of the pulley. C=PI*D Then divide this by 360 to assess the degrees of the marks you made. Jim

rustred · Jul 11, 2017

i am quite sure the timing is the same place at cranking speed as running speed. that was the whole idea of the manual retard lever. and so u dont get kicked when starting it. also if the impulse is not working it will kick you.once working and rev'ed up you manually advanced the timing. the impulse is there to get a hot spark for starting. this is on an E4 magneto. now got me thinking about the F4 magneto with out the retard lever.

teddy52food · Jul 11, 2017

Depending on the drive cup it would retard it up to 35 degrees. Not sure on the F4 mag.

steelfronts · Jul 11, 2017

The running advance when first started will be the degrees on the crank that the impulse coupling holds the mag still from catch to release

F-Dean · Jul 12, 2017

If you fully retard a F4 mag, the engine will not fire! You have grounded the mag!

F-20 Magneto Mysteries? for Nebraska Kirk, Jan Nicholson

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