UPDATE:
1.) Trimmed spark plug boot a sliver to ensure it is seated.
2.) Re-installed all plugs
3.) Checked for spark (grounded on valve covers) nice, solid blue spark.
Took it for a test ride.
STILL snap crackle and popping until about 4k rpm.
STILL stumbling and sounding the crap.
Looked at problem plug - dry and no black carbon.
You problem sounds kinda like mine, although mine is not as bad as yours. Mine is only from a stop trying to get going it sputters and I have to rev the motor to get enough rpms to take off.
I am planning on doing the "Shotgun" have you thought about that? maybe it just gunk in your carbs?