Have the governor removed, can see the butterfly valve. It is in the open position by default and can feel spring tension on it when pushing it closed. Can blow in the vac tube which tries to close it, but not hard enough to close it all the way. Removed the triangle plate to view the plunger that operates valve. Plunger conceals spring. Think it needs adjustment? and how do I access it?
Update: Found adjustment spring, phillips screw was loose on pivot and had moved slightly, adjusted screw and tighted, then put a little more tension on the spring. Problem Solved!!! Thank you for your help!

When l said check governor l did not mean spring in carb l meant under carb there is a governor with a butterfly plate that controls the rpm so the engine can't over rev.it is set at around 2600rpm unless it is a computer truck it has a spring inside that might be broke or need adjusting. The hose I think you are talking about goes from the govern to the air cleaner it is open to the air. The hose is approx 5/16 what you are doing is holding open the plate so the truck runs with your finger on the hose

Yes after replacing the Imco regulator and new diaphragm/spring in the carb, it did the same thing.
With hose from air cleaner to valve cover disconnected, I plugged the end that attaches to air cleaner with my finger and it was able to build vacuum on my finger and on the small vacuum hose that attaches to the top of the carb. Can now accelerate just fine until I remove my finger? Seems like it needs a pcv valve in the line to build vacuum but there isn't one there??

I would check govern under carb sounds like spring might be broke or need adjusting if you say engine is surging up and down