Re: another carb ?
Since I tend to be a bit anal and obsessive compulsive, I have NEVER mixed and matched carbs on a three cylinder engine.
If the number on the flanges are the same, they will work well. If the numbers are not the same, they will fit but offend aesthetically. There is also the possibility of engine damage. The two 105 carbs are usually WB with a 1 5/16 venturi and the 90 is always a WB carb with a 1 5/16 venturi BUT---They are jetted differently. Try to find another 105 carb if you really want to use them
EDIT: Do not expect a horsepower gain using the larger carbs--aint gunna happen.