340 Gets Terrible Gas Mileage

Back to basics. Dragging brakes can cause high fuel consumption. So lots of things to check. Start with the most obvious, the carb. Make sure the met rod pistons are free to move up & down. With met rod piston cover moved to one side, but still containing the piston, make sure the piston is down at idle & not moving. If it moves, it means the piston spring is too strong.

Check float level [ 7/16"], & that n/seats are sealing. Those carbs have plugs in the base that block passages that have been drilled during manufacture. Check that none of them are leaking. No gaskets are needed if you are careful.