The checklist of solving your problem would be very long. What you should check and I would be surprised iI I was wrndng iI make sure all your air hoses including vaccum advance lines are on and have not come off check the hoses are not cracked or split If your motor iI fitted with a air breather valve check it and also the hose Sounds like air is being sucked in when motor is running causing iI to over rev. Good luck
Nick Coudounellis
October 2013