Yup. That's the big clue its too lean!
Throttle position and load determine when the main circuits provide the bulk of the fuel into the airstream.
There has to be enough throttle opening and rpm that the air velocity creates a strong low pressure in the boosters.
2400 rpm at 30 mph might not produce enough load (wind resistance mostly) to the car movement to neccessitate much throttle opening.
2400 rpm at 65 mph probably will have enough resistance to the car moving that it does require enough throttle to bring on the mains.
Hesitation from a full stop is not related to the mains. If it happens with slow opening, then its "idle" circuit.
