What does it mean when it start smoking heavy out of muffer

Check oil level.
Make sure its not over full'
Gas could be getting in your oil through carb , valves .
If oil level okay could be piston rings , or could be head gasket.
Luck

All of what DG stated. Only thing I would add is that the crank case breather my be stopped up or you could be using the wrong oil. You are supposed to use 30 weight non-detergent oil.