Yep, the cap does help keep the screw in place. people have said a drop of sillicone helps keep it in place without the cap.


best thing to do right now is to carefully count the number of turns IN the screw goes until bottoming out. That will give you a base number to work with. Problem is there are a few different specs for different carbs.


The other thing is that will only really effect idle mixture. once you gas it the idle circut cuts off.


Carbs are also mechanical will passages and jets that don't really get bigger with time. The see very little metal/metal wear. Rarely is the carb at fault for being rich. Remember, a rich situation can be caused both by too much gas, or not enough air.