1940 John Deere B Timing+

So, I got a chance to run the B with a timing light and from the best I could see (cast back rims are impossible to see through) it was running around 18-19 degrees. I will be putting the governor gear back to the correct position later this week and reusing the timing light to see where its running again, I did turn the magneto back CCW as far as it would go, which changed the timing to 5 ish? degrees I think, which is exactly what you all said would happen. so if I put the gear back to where it belongs I think the timing will be too far in the other direction(30-40 degrees) so this must mean that my drive cup is wrong, right?
It could also be that the mag assembly was not quite to spec. I'm not certain of the Wico "C" series but the "X" series had a D-shaped rotor shaft and the flat and/or its mating drive plate could be worn and not reliably fitting exactly as designed. Remember that 2 degrees at rotor/point end of the mag is 4 at the crank, so it wouldn't take a lot.

This post was edited by Watthour on 03/07/2023 at 07:50 am.
Well, I had a chance to mess with the B again this weekend. and after using the timing light, here's what I have found.
On a 25 degree Drive Cup.
Governor gear in correct alignment: 28-40 degrees TDC
Governor gear 1 tooth CW: 20-30 degrees TDC
Governor gear 2 teeth CW 5-18 degrees TDC
I put the gear back to 1 tooth off, and i think I'm going to leave it there. I'm thinking JD39B was right on me having the wrong drive cup, or at least that's what makes the most sense to me anyways. I don't think I'll invest in the other drive cup seeing as I have it running at around 25 degrees currently with room to move the mag either way. I'm also thinking I might need to just put more running time on the rebuild like we were talking earlier to make it run better yet. It seems to be running better all the time so after I figure out why the PTO lever is jammed and wont engage the PTO, I'll put some time on the dyno and really get it tuned in.
Thanks for all the help everyone, really appreciate all the insights and helpful comments. I think I'll stick around this sight for awhile!

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