Does your KTM use a PVL ? if so PVL only suggests one plug type.
use that over any Ktm books spec, if its digital it needs a 500 ohm plug and if i remeber its a gv not a egv or somthing similar.
Was the bike pre delivered correctly ? as in is the earth on the coil on metal or is it not earthing propery somwhere under there and shorting out the plug only to re-earth properly when you mess about under there , then moves back to an unearth when its ridden over bumps etc again.
I like the thinking on the blocked carby pipe, come unstuck a few time on that one. if the plugs not fouled then it could also be just ign problems, tell the dealer you want to borrow another coil and black box to eliminate it, my gut feel is there is a gremlin in the ign and its shorting plugs. i know if i over rev my 360, particulaly if its in neutral trying to clean out the pipe, it kills my plug, it will missfire and wont rev out during a race, new plugs fine, and only ever happens if i over rev the dam motor, if i dont it goes for eva.
just some thoughts