You have to figure out if the problem is on the motor itself or in the throttle connection to the motor and/or shifter.
Disconnect your throttle cable from the throttle lever on the engine. Part #2
http://www.boats.net/parts/search/Honda/Outboard%20Engine/2002/BF75A2%20LRTA%20/SHIFT%20SHAFT/parts.html
Then manually advance the throttle lever, part #2 with your fingers and see if it will go all the way to touch part #10. Check the other side of the engine. When the throttle lever is touching the throttle stop, then on the other side of the engine, the roller cam should be all the way to the end of the slot inside part #17.
http://www.boats.net/parts/search/Honda/Outboard Engine/2002/BF75A2 LRTA /THROTTLE CAM/parts.html
If the throttle lever touches and the roller cam goes all the way up the slot, then you just have to adjust how the throttle cable is connected to the engine and/or the shifter.
If the roller cam does not go all the way to the top, then you will have to adjust cables #1 that go from the port side to the starboard side of the engine. These sometime are not adjusted right after someone removes the carburetors.
When you get the throttle lever to touch the stop, then reconnect the throttle cable from the shifter as follows.
At idle (shifter in neutral), the roller cam that rolls inside part #17 on the other side of the motor
http://www.boats.net/parts/search/Honda/Outboard Engine/2002/BF75A2 LRTA /THROTTLE CAM/parts.html should be centered at the little arrow near the bottom of the slot.
Then you have to adjust the brass connector at the end of the shift cable to just fit in the inside hole on the throttle lever Part #2
http://www.boats.net/parts/search/Honda/Outboard Engine/2002/BF75A2 LRTA /SHIFT SHAFT/parts.html. Do not put it in the hole at the end of the throttle lever.
If everything is ok at the shifter and you have the correct shifter, the adjustment above should give you full throttle.
You can see if you actually have full throttle by either checking the throttle stop or looking at the cam on the lever on the bottom carburetor.
Hope this was not too confusing.
Mike