1982 Yamaha XS400 Seca Idle Issue

2.5 turns out on the idle jet screws is really just a starting point. You'll want to keep adjusting them out slowly, I usually do 1/4 out on each side and the idle should raise further each time. If the idle gets too high, adjust the idle speed screw back down to 1200 and continue the idle jet screw adjusting until the idle drops. Then turn the screw back in that last 1/4 turn and set idle speed again.
The hanging idle response to the slight throttle blip and the increase without throttle shown in the videos is an indication of a lean fuel mixture. Adjust the pilot mix screws as indicated above by @tstidham to establish the proper idle air/fuel ratio.