If your timing is correct and the ignition is up to par the plugs will clean themselves I never had any good Champion plugs so I would start with Denso,NGK, or Accell plugs.Some swear by Autolites I like Denso Iridium plugs,they never foul with MSD and Firecore ignition components and they don't wear out.
I have also seen this type of problem with the cam timing off the mark
If you have anyone local to you with a 440 try the ignition system off their car and see if there is and difference,or you could also just try another carb
Sometimes you have to know what it isn't
Gus