It has new rings now, but I never had it running before the new rings.
Compression 98 & 95 psi, which is about the same as my KS-15
that starts easy.

Went through the magneto, did a coil swap for one cylinder, new capacitors.
New sparkplugs showing nice blue spark.

Carb throttle spool / valve may be a little sloppy, but maybe that’s
just the way they’re made. I tried swapping carbs with the KS-15,
but they’re different, and won’t swap.

I switched magnetos with the running KS-15, and it acts the same,
like it’s only “hitting” every once in a while. I tried enriching both
high and low speed needles, which didn’t seem to help. When I choke
it, it seems to be getting excess fuel and will quit firing.

Before swapping magnetos, I removed the carb and poured some two
cycle oil on the center crank, turning the motor over, with the motor “horizontal”
so both sealing rings should have been good and sealed.

If it’s the crankshaft sealing rings, I’m guessing I’m “out of business”…..
I have no other good ideas!

P.S. – While the motor was apart, I checked, and rodded out the exhaust passage
in the lower leg, and it seemed okay.

VIDEO of Failed starting attempts with know good magneto

https://youtu.be/jkidXxzdjEg