coil + ballast resistor

Sorry 2 important questions i ommited:
As some systems run without the ballast resistor the coils must be getting an unstable power source of up to 14 volts, is this really ok as long as the coils are of sufficient resistance to protect the ignitor, ta- mat
Also with a weak/intermitant spark could one effect be that the engine revs cleanly under no load, but under load will only run smoothly to a certain rev range (in my case around 5000 rpm) after which it misses and bogs etc. Just wondering if this definatley indicates my mix is out as well. . . . . . . . . .. . .... . ...

12 to 14 volts is fine. The coils won't care about the stability as long as it's in that range.

Usually, assuming the spark is reasonable, and timed correctly, the strength of the spark should not affect performance noticeably.

If it does, that is usually an indication that the mixture is not right-on, or the engine has some condition issues.

cheers for help, running the old 4 ohm coils now without ballast - much better spark, carbs are well out - about to write post on carb page concerning this..........