1979 20 hp mercury thunderbolt ignition help

[WalleyeBob83]

hello,
I have a 1979 mercury outboard 20 horse power thunderbolt ignition. I've been having a lot of issues with it for the past couple years now. The engine runs but starts hard and seems to lack power at lower rpm range. Last year I replaced the kill switch and the switch box due to the wiring getting rotted and shorting to the engine block. it has also had the carb. rebuilt and it is spotless inside. I've always used non oxy gas in the motor. I took the motor to a outboard mechanic last week and he replaced the water pump he said the old one was worn out, also he tested the engine compression one cylinder is at 120 and the other is at 116. It has good spark and is getting sufficient fuel to the carb. The mechanic replaced the transfer port gasket and small oiling hose on the right side of the engine block due to leaking. I replaced every fuel line on the engine from my tank to the carb also replaces primer ball and connectors. The motor seems like it is maybe running lean to me because if I choke the thing it seems to run better but still not correct. Does anyone have any advise for me or things I can check to make this run correct again?
I'm at wits end with this thing I just want to get out on the lake and go fishing again.

Thank you in advance,
Bob

 

[WalleyeBob83]

the mechanic also stated I might need to adjust my throttle linkage? but he didn't know how to do this exactly so he didn't mess with it. I don't see how that would cause my issues but I guess it might. I've had the engine die a couple times also while going across the lake and at times I've been at wide open throttle and it seemed like I was at half throttle for awhile and then it would just clear itself up and run fine again. At the times it acts up like this the motor wouldn't have enough power to even plane the boat out.