Yeah, my xp is acting similar. From what I have read so far, I think the pop off pressure is too high, but in your case, it could be bad needle/seats if it smokes alot on startup.
My suggestion is to check your pop off pressure and get a carb rebuild kit and start there. Also make sure you have replaced the old grey fuel lines (read up on that, it's posted all over) and cleaned your fuel filters in the line and in the carbs. Also it might not hurt to do a crankcase pressure test to see if your crank seals really are bad.
Anyway, my two cents on what I have learned so far. Correct me if I am wrong or if you have anything to add Doc.....
:cheers: