I received a 1978 CB750K from a good friend of mine. It had sat for 19 years. 12K miles, looks like brand new.
I got everything OK, except the idle circuits. It was HARD to start and would not idle for anything.
So, I removed the fuel line from the tank petcock, drained the float bowls then closed
the drain screws..Used a very small metal funnel (Ebay) and placed it in the end of the fuel line
and filled the carbs with Sta-bil Green (marine) until the fuel line was full. I opened the idle mixture
screws to 4 full turns out. I let it sit for 48 hours. Then, I hit the starter with choke on and throttle closed to
create maximum vacuum. Did that 4 or 5 times for about 10 seconds each. Topped off the fuel line with
Sta-bil green. Let it sit another 48 hours. One more shot with the throttle closed and choke on.
Then drained the Sta-bil from the float bowls, reattached the fuel line to the petcock and turned on the go juice.
Reset mixture screws to 1.5 turns out each.
Hit the starter button and the engine started right up with a good idle. The accelerator pump even works, now.
Your mileage may vary. Hope this may help someone.