1967 65 HP 4 cyl Runs great at full throttle then

[signguy295]

Hello,
I just got this 1967 65 HP 4 cyl Runs great at full throttle for 3-5 minutes then its like someone hits the kill switch for a second, then it will pick back up for a minute maybe two then she will die out to just above idle speed. She wont quit she just wont throttle up again. It will run all day if i dont take her above half throttle. what I done so far is new gas tank new fuel line new plugs new impeller and new wiring harness. One thing I didnt change was the mercury switch and wire,How important is this or whats its purpose. Any ideas will be appreciated
Thanks John,

[mercmafia]

I would start by cleaning the carb because it sounds like it is clogged up really bad.