Problem with Mighty Demon 750

I'd put a proper power valve in there as well. Get your timing set. Rebuild the carb to stock using a rebuild kit. Generally these kits return the carb to exactly how it left the factory. And usually that's pretty close to what you need anyways. Make sure it's all clean and sparkly. Then tune for best vacuum. Now half that number. That's your new power valve number. Get those power valves. Then all you gotta play with is jetting/pump etc. Fine tuning from there basically.