Carb....
Advancing the carb throttle without the timer?.....well not sure.
Spray something like carb cleaner or propane into the carb shaft at idle and report.
Might just be a bad carb.
What specific linkage are you talking about.
https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1996&hp=150&model=E150EXEDB&manufacturer=Evinrude§ion=THROTTLE+LINKAGE
You could also try eliminating the control box as a problem by starting it, disconnecting the red plug at the motor and see if it's still a problem.
Are your butterfly's opening all the way? I'm thinking they are.