The bottom screw (Lo adjustment) is not to be used for throttle response.
First of all, put the boat in the water on a trailer (pump in the water)
Start the engine and let it idle.
Adjust both low speed adjusters to obtain the highest idle possible (without touching the throttle or anything like that)
Then take out the boat, run at 1/4 throttle for about 30-60 seconds.
Then gas it and see what happens.
If it stumbles, you need to increase the pilot jet size.
If it simply doesn't rev and takes a while to clear out, you need to decrease the pilot jet size.
Once you have that sorted out (and jetted properly), repeat the low speed screw adjustment.
Then go to 1/2 throttle and cruise at that for 30-60 seconds.
Gun it, see what happens.
Same as above, adjust your mains accordingly. You don't necessarily have to rejet here, you can use your hi speed adjusters.