Re: 1940 Johnson HD-15 Magneto testing

[joesnuffy]

If bakelite and tab was off 120 degrees to the left looking at your picture then engine will still fire at 0 degrees and 180 degrees because points lobes are set in stone on flywheel or points cam. (points cam upside down? then where would engine fire. Since 2 lobes might not make a difference)

One brushes would make contact with tab in flywheel at 320 degrees to 40 degrees which allows a 0 degrees fire with 1 cylinder grounded Then at 140 degrees they contact tab in flywheel has contact with other brush to 220 degrees and allows fire at 180 degrees with other cylinder grounded. That would allow engine to fire while 1 cylinder is killed by a brush on each stroke.

It would be nice to see a pic of the flywheel tab in correlation to the flywheel key. Hopefully someone reading this has one so we can rule that out. I’ve looked all over internet can’t find one.

Also after I looked at your some of your pictures I see the throttle advance moves to the right for faster so engine would spin clockwise more than likely. It would have to move to the left for faster if counterclockwise.

Joe

ps I am guessing if you got double fire on both cylinders after checking bakelite could be off 120 degrees or points cam is upside down which I don’t think would make a difference since it has 2 lobes but worth checking.

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