My 340 getting 6 mpg

cojohnso said
MPG is tough. My right foot dictates. 16 MPG is the best I can get on very modest highway driving. Stockish 440 4-speed B-body running Dana 3.54:1 with talker 28" rear tire. But just a couple fun thumps on the pedal and suddenly drops to high single digits. Or worse if nonsense continues. Lol.

My 440 is running single pumper 750 Holley. I found for best performance and economy? The smallest carb that still gives you the needed CFMs at WOT. Faster throttle response with better fuel economy.

I would think the 340 as described? A 650 spread bore may do that job?

16 for a 440 is pretty good. Too bad the OP isn't getting that. Speaking of the op, he needs to forget about mileage until things get broken in and loosened up. In the meantime, look at some simple things like make sure the choke is open and pull a few plugs for a look see. That bad of mileage, you should see some black. Another question, how are you testing your mileage? Fill the tank, write down the miles on the odometer. Drive around how ever you want. Town driving with a hot rod and mileage sucks! I would put 50 -100 miles on it of combined driving. Drive it easy not like a crazy man. Refill the tank and record the gallons used. Divide that int the miles traveled and there's your mileage. I worked at a dealer for 13 years and you can't believe how many people don't know how to check mileage. If there is an excessively rich issue, itt should be corrected now before you do some engine damage.
A friend had a stock fuel pump putting out 8+ pounds and the carb was bleeding over. That could be an issue. I think I read some discussion about timing. SOmething else that needs to be right. (including the advance)