All carburetors function under engine vacuum - regardless updraft/downdraft configuration - unless they are turbo-charged; and even then vacuum plays significant role. The piston adjustment to which you refer is part of the carburetor accelerator circuit; one of five such systems contained in that device. The piston only moves during sudden drop in vacuum (or on some carburetors in combination with designated linkages) hence the 'accelerator' descript. Normal - not 'lead foot' - acceleration does not see that circuit operate. However, on a rough road, with your foot jabbing the gas pedal yes, conceivably, there could be unintended spurts of gas emitted from that system. But, under smooth acceleration and steady speed such does not occur. Setting for pump stroke (the three holes) simply allows more - or less - fuel to be introduced into the carb throat upon stomping the gas pedal. I don't see excessive gas consumption there. And a COE is not really a candidate for jack-rabbit take-offs. :o)
The vehicle's gearing, as mentioned by Harvester, bears directly upon its fuel consumption, as does its overall weight. As you've indicated, there appears nothing amiss with the fuel delivery system, brakes, air filter, leakage. My only suggestion would be a tip I received from a RV owner: "Drive as if you've an egg between your foot and the gas pedal." I tried that - wiped up the mess - then installed a vacuum gauge. Keeping its needle in the green zone is half the fun of RVing. And with gasoline up here currently at $5.53 per gallon (and rising) I am very cognizant of fuel wastage. But every little tweak is bound to help and, as mentioned, that's the challenge of driving a Big Bolt. Good Luck with COEy.
Laurence
