[Chevy-SS]

Sounds like you built a gas-guzzler engine there. Big cams always drink a lot of gas, that's how they produce more power.

Do you have access to an A/F ratio meter? If you have a buddy in the inspection business (depending on your state) he might have a wide-band O2 sensor that he could stick up the pipe while you experiment with different jetting in the carb. Holleys are easy to tune just by switching jets around. I think your carb uses different metering rods to affect changes in the A/F ratio. It's kind of a pain to adjust, but sounds like you need to do it.

Another thing to check, which may end up producing the best results, is the timing. With an engine like yours, I always like to use a standard HEI distributor with vacumm advance. I usually set base timing at idle (vacuum advance disconnected) at about 10 degrees advanced. Then I connect the vacuum advance line to a port on the carb that has full vacuum, even at idle. That way you will get about a 20 degree advance in timing at idle and this will really help smooth things out. Also, you will get significant timing advance under normal driving, which will really help mileage. Just make sure that the vacuum advance decreases under heavy load, or you will hear heavy pinging and could damage the engine. You can check this by using a timing light: watch timing and hold carb (by hand) at about 1500 rpm, then give it abrupt throttle and you should see timing decrease as vacuum lowers. If not, then select a different port on the carb.