Those red and white plastic caps are limiters, which are designed to prevent you from adjusting the carb beyond a relatively narrow range. This is done to control emissions and make the engine run leaner than in old days. This is required by EPA and CARB.

Usually the red cap is the high speed (main) jet, and the white is the idle mixture. On a Walbo or Zama carb, the main jet is furthest from the engine (nearer to aircleaner).

For both jets, turning counter-clockwise richens the mixture. However, if you go as far as limiter allows, and still need to be richer, you'll have to take to a shop where they have tools to remove caps; make the adjustments; and replace caps.

I just took needle nosed pliers and pulled one of the limiter caps off, adjusted the saw and reinstalled them. I still maked the orginal location of the jet splined end (not the limiter cap) before adjustment in case that wasn't the problem. you may have to pull the other limiter cap off and reindex it to match or align up with the hi if you want to reinstall limiters.

There other ways around this also. Proper splined adjustment tool. removing the screws cutting slots in the heads if you don't have the proper adjustment tools.