You have proabably broken your rings and need a rebore. At the very least!
Basically the rings act as a seal for your oil and petrol mix. If your rings are broken or the bore is scored and marked this seal wont be there and you will be getting too much oil and petrol to the plug... hence a tonne of smoke and probably crap performance. Only way is to strip top end and check rings and bore. Not a terrible job but its only for those who know what they are doing.
bb
May 2010