if its sucking air through your tail pipe i would check and see if when u try and start the bike if the carb pushes gas into the breather then you know their is either a whole in your piston, rings are shot, or your intake valve is stuck open and the head is pushing air instead of sucking from the carb and out the tail pipe. compression problems could be as simple as no plug in the bike bad piston bad rings anything of that nature check your carb and see if its pushes gas into your breather when you try and start it then let me know what happens.