could you explain what you mean by you " adjusted the carb accordingly"?
was it fuel fouled or oil fouled?
main jets can come lose and fall out, then it falls on it's face on the top third.
allot of the time a weak spark will cause problems when combustion pressure is high [ high load, lugging, or off idle] not to say it's not your problem but weak spark in it's self shouldn't foul a plug.
you can get spark testers or make your own to see how far or strong the spark is... just be care full it's not to far as the coil won't be able to discharge properly [ jump the gap] and it's possible to damage something else...
here is a spark tester, you unscrew it to increase the gap and see how strong the spark is.
Ignition Spark Tester with Adjustable Gap - 404, by Thexton