1990 is the year.

I thought there was a point with backing the air screw out that it should rev down again or is that wrong?

Also when setting the slide height, do you set that height with the idol adjustment on the side of the carb, or open up the throttle on the handle bars and adjust it there? Also do you measure where it's flat when looking into the carb cause the middle has the round part on the slide that goes higher?

Pro,  the more you back the air screw out, the more air you let in.

Use the idle screw (thumb screw) to set the slide height.  Be sure that your throttle cable is adjust correctly so that the slide is able to go all the way down.  after setting the slide height, adjust the throttle cable so there is no slack.

Pull the boot off connecting the carb to the air box so you can see the slide while adjusting.  again, be sure that the throttle cable is adjusted out so that the slide rests on the bottom of the carb.  From there, screw in the idle screw until the slide raises about 2-3mm like Ice said.