partial loss of engine power due to a fractured number 4 exhaust valve, which resulted in a forced landing; and the lack of sufficient airspeed to maneuver over power lines during an attempt to abort (go around from) an emergency landing, which resulted in an inadvertent stall and subsequent impact with trees. Factors relating to the accident were: the owner/operator's failure to perform the engine manufacture's recommended overhaul at the recommended time, and high obstructions in the emergency landing area.