Deva, LA isn't a tuning screw other than for the idling rpm adjustment. If it is merely a carb adjustment problem, the L screw is probably what needs to be dialed in. Don't lean out the H screw too much or you can ruin your saw, that's not really a concern with the L screw. The factory specs for the screw positions should get you pretty close if the saw is otherwise in good running order, but age, worn out parts, and time of year can affect the final best settings. The LA screw is usually the final adjustment to get a good idle without the chain moving. Worn out clutch springs, not uncommon on older saws, can have the chain moving at what would otherwise be the ideal idle.