Mixture screw on Carb

It could be a sticky or misadjusted throttle cable. Or a stuck slider spring.

Each carb has a small vacuum port on the side above the float bowl, you adjust the idle stop screw to set the tune and sync the carbs. Leave the air fuel mixture screws alone.

The mixture adjustment should be for idle or idle fuel mixture. Even if that mixture adjustment is off, that will not stop it from making power in second gear. If the motorcycle has been sitting for more than 6 month without being run, the carburetor and fuel system probably needs cleaning.

Why did you need to clean the carb? Routine servicing of the aircleaner would keep the carb clean for life. The pilot screw should be 1.5 turns out approx. with a small adjustment either way. Idle speed is set to a smooth low idle.If this doesn't fix it have you got something in the carb not replaced correctly? The float needle/float assy? How did you clean it? Have you introduced fluff/dirt into the carb and did you blow it clean with an airline?

clockwise for leaner mixture( it's really and air/fuel mix)

should be a mixer screw on carb.

On most Mikuni carbs The screw that lines up with the middle of the slide and often has a spring on its shaft to stop it moving is the idle screw, it merely lifts the slide to increase engine revs, the same as opening the throttle and will not change mixture or jetting.

The smaller screw often on an angle, or from underneath is the mixture or air screw. this will affect mixture mainly at idle, low revs, starting.
these are usually set by screwing it all the way in and counting the turns, then back it out the same number of turns to get a start point, usually about 2 turns out from the fully in position. it should only need adjusting about a quarter of a turn either way.

with the bike idling as you turn it in, the engine will start to bog down (rich) as you screw it out the engine should smooth out until it has an uneven idle and change in idle speed up and down(lean) and pick the smoothest idle in the middle, but this should be less than 1 turn from rich to lean

restrict the air flow to the carbs it will not bog out