The workshop manual for your CB750K 1977 will not help with the carbs.
If it has the accelerator pump feature you will need to get online help.
There is a bottom plate on the accelerator pump and there is a check ball with spring in it.
If that part does not work your carbs will never function correctly.
There is another check ball in the float bowl top edge that keeps fuel from
draining backwards but that check ball is usually not a problem.
If the carb float bowls are full (engine NOT running) and you actuate the
throttle, fuel should squirt out of all 4 brass tubes sticking up inside the venturis.
If not make sure the interconnecting tubes and brass spray tubes are not clogged.
The rest of the carb is cleaned the regular way. except the brass
idle jets are the push in type.
HINT... IF they are push in then they can be pulled out. Remove the
floats first so you do not damage the float.
On a Roadstar Adventure.