I pulled the old beast out of the shed after of many years of not running.----------You answered your own question with that statement . It sat for many years and more than likely the carbs' innards are stiff as a board .
What happens more times than not with a shelf sitter is it might run for a day or so then it's about like the carb gets full of concrete .The thing stiffens up and it refuses to start ,it might idle and it might not .Rebuild the carb it will run more than likely .