I am trying to tune the carb on a Yamaha 80 raptor. I do not know which screw does what. By the way, this is NOT a G5. It is a small 4 wheeler The carb is a Mikuni G499? or a 5TH1.00? HELP Please !!!!!!

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