One respose and I didn't have to look to know who it would be from and of course am pleased that it was you-although all responses are viewed with gratitude. I guess what I mean by strong spark and since I have no idea how the spark from a coil is measured or even what the system of measure might be I'll just make one up. Let's sat that a coil with a "strong spark" measures 100 on the franklin scale (about the same jolt of electric current that Benjamin Franklin got when he lofted that kite of his in a storm, causing the sloes of his shoes to smolder) As the storm abated, the intensity of the jolts did too so only his eyeballs lit up. The coil is new and produces 100 on the franklin scale. The observer of said spark sees a brilliant, bright blue on his test plug. At 50 the blue is now a pale yellow. I guess that's what I mean. So let's say I pull the big wire out of the distributor cap and hold it away from same as engine is runnig, a long blue spark should appear across the gap, like the thingamagig in Frankenstein's lab.

This has zero to do with this but i had a coil once that would be fine at start-up, but after everything warmed up-and not always at the exact same interval-the engine would just die. Wait 15 minutes and it would start again when it cooled off. Took me a while to figure out what was going on. It was a 1951 MGTD so it had a Lucas coil, that should have been a clue right there.