Why do you gave an unstable idle? I ran a bigger cam with an 800 avs in similar cubes and still managed to get 9 inches. If your idle is fluctuating you need to find out why.
Have you checked your plugs?
have you check your leads?
Have you done a leak down test to make sure all your valves are sealing.
You can try another carb but I don't think that is the real issue here.