I had this issue years ago and I'm pretty sure I had the butterfly linkage hooked up wrong, surprisingly when I got it hooked up right, there was just a very small increase in performance.

Thanks LiquidLounge, I plan on taking a much closer look at the linkage this weekend to see if i have any options there. I'm pretty sure that there was only one spot to attach the pivot bolt in the linkage to the throttle body, but i may have been mistaken.

I will report back to this thread in case it might help anyone else considering this in the future.

Quick update:

Upon looking at the throttle body more closely, there is a small stainless steel extension on the linkage that moves the butterfly. I think if this 'extension' is removed (it is bolted on) and attach the cable at that closer point to the pivot of the butterfly, that I could decrease the throw required to go from idle to full open significantly although I have not tried this yet.

I went ahead and measured the throw of the Livorsi at its longest throw pin and it was only about 1/16" less throw than the Mercury Zero Effort control that I had in the boat, so it is likely that the zero effort never allowed the butterfly to go full open.

I hope this helps anyone trying to do the same project in the future.