The main problem with the 1977-78 accelerator pump system is the check ball in the bottom plate.
It can get corrosion from moisture sitting in it, and then the check valve ball will not work.
The ball can get pitted and the seat also.

There are two check valves , one in the top edge of the float bowl that keeps the fuel from draining back down into the bottom and one check ball in the bottom of the pump. IF the check ball in the bottom of the pump does not work, nothing will work.

Do not lose the small black rubber o ring that sits on the top edge of the float bowl.

The Clymer's manual talks about adjustment of the pump rod but it is all nonsense. The tang that the pump rod comes up against is so thick and strong forget about adjusting it. Not possible unless you are wiling to damage the carbs to do it.
When you see it you will realize there is no way for it to get OUT of adjustment.

Make sure the spray nozzles in the venturis all work.
Get a bright LED pocket flashlight and with the engine OFF and the gas on twist the throttle  a couple times and at the same time watch for a squirt of gas from the spray nozzles. If clogged put some carb clean through it. All 4 of them.

Also the rubber tubes connecting the carbs for those accelerator pump nozzles contain two small brass tubes to restrict the diameter of the tube. There are two so that they can be fitted in that small space.
If you just throw away the black rubber tubes and replace them, then you will not have the same pressure to the nozzles, because you will have thrown away essential parts.

I don't like the whole accelerator pump system. Band aids over band aids.
If you want the best deal get some 1969 carbs. They really respond to adjustment.
The 1977-78's were the worst carbs in my opinion. Too complex.The so called lifter arms added a lot of weight to the carbs and then you have to completely remove the carbs to work on them. Then there is the "press in idle jets" 

Shall I go on? No