Quote:
Originally Posted by Wisakedjack
... I checked voltage on coil '+' terminal when cranking. It was just below 9V on last try. ...
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This seems way too low. When you checked the spark, was it a snappy blue one or a weak yellow? A weak yellow spark in open air will likely not fire under compression, as the breakdown voltage of the plug's gap goes up as the pressure goes up (
Paschen's Law).
12V on the unloaded battery also sounds pretty low too.
Since you have a ballast resistor, one trick you can try is to use the normally-unused "R" terminal on the starter solenoid. This terminal has a direct connection to the battery "+" during cranking, and is open circuit at all other times. If you connect it directly to the coil's "+" terminal, it will bypass the ballast resistor during cranking (when the voltage is at its lowest) giving you a hotter spark for starting, then revert to normal while running.