If the tank is completely empty than it must just be a that your engine is tuned way rich for break-in and running full throttle to have enough power, once it breaks in trim up the fat and then you'll only 1/4 throttle to pull the lt-40. your fuel consumption will improve dramatically.
Like I said my ax46 seems to go like 1/2hr. on 14oz, 5 mins would barely put a dent in the fuel, are your helpers playing with carb settings 15mins before putting it up or what?