2 stroke will not rev out

SOURCE: Aprilia RS125 doesnt rev past 5000 rpm

not cooling properly

SOURCE: aprilia af1 125 sintesi, carb settings, what are

Hi and welcome to FixYa,

Jet size would depend which carb is installed, a Dellorto 34mm?

Initially, check the sparkplug tip colors. If very light brown to almost whitish, then lean mix; too much air, too little gas. Try raising the needle if if has notches and moving the e-clip. If fixed, use small thin washers. The basic idea is to make the needle rise early on throttle movement.

If an aftermarket open breather air filter is installed, then it would be causing the lean mix, too much air. Restrict the filter by adding temporarily upholstery foam to experiment at which thickness the flatspot would disappear.

Good luck and thank you for asking FixYa. Happy Holidays.