Or fix the 4777. There's really nothing to wear on it. So if its 'shot' in that its not running right but it used to, then its something simple; Dirt in passageway, leak from accelerator pump, umbrella tytpe check valve distorted from fuel component, etc. Take one apart and you'll see there is nothing to it. Don't touch the idle 'speed screw' and the only tuning you'll have to do is the idle mix screws. Get Ulrich's 4150 book or Ulrich and Fisher's Holley Carb book if you want to know the basics of how they work and the various parts.