I replaced a carby a while back, got a new one from USA and the saw ran sweet ever since.
That old carby I stripped and rebuilt 5 times, dealer had it twice I think.
The saw had a flat spot just as you hit the throttle and it would die, then be a bugger to start.
Anyway, I sent it over to ole Al Smith just so he could see what was going on out of curiosity. Ends up it had a hairline crack thru it that would expand when hot and run lean. That totally supports your experience as it would have been the alloy casting fault.
My brand new 200T had it's own unusual carby problem. The throttle linkage would get caught on the carby and lock onto high revs! This saw was like this new. As I bought it from USA I just got some long nose pliers and rebent the throttle linkage ... but I had to strip the carby off to do it. So something is definately changing.
I prefer my old 200T @ 2001/2002 to the new 2006 one. It somehow just feels better, tougher. The new one broke a starter cord like within a month, the old one had only done that after a year. There's something changed for sure.
The old one is bogged up with Selley's knead it epoxy compound to stop oil leaking out etc from cutting palms.
I just cant put it out of it's misery coz it goes so hard and smooth, but it does have a replacement USA carby on it 2005/2006.
But I must say, after a husky 335 I'll take the 200T with it's problems any day.