1985 XR100r spark but no spark

A little back ground on this bike then to my query. Picked up cheap 85’ XR100r for my kid. After a lot of fiddling it did run but very poorly. Cams and rockers turned out to be destroyed from lack of oiling. Took the top end apart and fixed that problem and replaced rings now oils properly and has great compression. Reset points gap and valve clearance. Check for spark now and no spark. Pull the plug and insert a spark tester from spark plug cap to engine case and lights up beautiful with each kick. Try a different known good plug from a running engine still no spark. Swapped in a new coil, same result. Can anyone out there think of a reason this is happening? Please help

How did you check for spark when you weren't using the spark tester?

Checked for spark by grounding spark plug to the head and kicking over engine.

Strange...

Is the head painted? Maybe there's enough overall resistance in the system to prevent the plug from sparking?

I had something similar happen while I was troubleshooting my FA50. It would spark with the plug grounded out to the head. I'd put the plug back in and get nothing while kicking it over.

It turned out to be the stator winding failing. So it may be worth looking into that.