85 Wellcraft Elan 4.3 surges HELP please

I have a 85 Wellcraft Elan 19' open now with a 4.3 merc and alpha one drive. My father in law actually sold this boat new in 85 and ran across it acouple years ago and purchase it with a cracked blocked. I installed a new 240hp crate motor from USA marine and boat has been an absolute joy for last 4 years and no problems.one day it started surging and docked it immediately went to carb that was leaking out of the accelerator pump. Did I light quick rebuild on dock and had to adjust the float a million times and when all done ran better but still surges. Can here slight miss at idle and then falls flat and can barely get in plane. Also will ad that can not get it over 4000 rpms at wot. This started a month before carb problem but ran flawless and use it for wakeboarding so speed did not bother me and thought I would address it this winter.since this I have had 3 shops and one mobile guy out and no answers. Under advice I changed fuel pump , filters and been through 2 new carbs and bypassed fuel tank. One shop said ignition so all new distributor , rotor , cap and thunderbolt 4 ignition module and none of these made a difference. Did compression / leak down and all is good. All over 151. Bypassed all electrical and just ran hot to ignition and turned off batt switch once started and had all wiring unhooked no change. Can a lower unit cause a motor to surge? Still feels like ignition? I thought it was the module since that controls rev limiter and advance but neither boxes made a difference. Timed it hundreds of time and no change and followed mercy advance curve and is perfect. Spent thousands on this and local shop will not test in water so I'm on my own. Please please help with any advice!