I ran a 12/17 c75 with 84 mm nozzle and smallest Tbm cone on my 144 pump. Now I run a 9/15 e-75 with a 90 mm nozzle and the mid size Tbm cone on my 155 pump. Same motor timing and carb jetting. I got the 155 to keep my motor loaded exactly the same. It helps when you can change tail cone volumes and slip in different reduction nozzle rings.
I would be trying 88 or 89mm and then increase tail cone size accordingly to stop any slippage and add quicker hookups. That is if indeed I don't have some other sort of engine tuning problem. A total loss will give you huge bottom end gains too so that may be the missing part of your current puzzle.
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