Tuning procedure, without tach.
As its ticking over after a fashion you are part way there already. Firstly tune the WOT with the H screw. Before attempting to tune, make sure the 2 line head is fully wound and the 2 lines are both extended to the correct length, as the length of line controls the max speed.
Rev the machine flat out for a minute or so, then adjust the H screw. Try it clockwise first. If the revs increase keep turning it clockwise until the revs peak then start to drop off (lean drop off point). Then turn slowly counter clockwise, the revs will peak then hold steady for a small amount of turn before dropping off at the "rich drop off point". Turn slightly clockwise from this point until trust before the revs start to peak. Leave it there for now. Don't start listening for "four stroking", this is a strimmer so is working under load even when not in work.
Now turn your attention to the L screw. Let the machine idle if it will and turn the L screw in the same manner as we did the H. First turn clockwise until the idle peaks and then drops. Then turn counter clockwise until the revs start to drop off and the engine gets a little lumpy. Then turn slightly clockwise until the idle smooths out. So we are close to the rich drop off point rather than the lean drop off point.
Set the Idle speed screw to give a smooth tickover a little below the point at which the centrifugal clutch engages. Repeat the L screw adjustment.
Let it idle for half a minute then blip the throttle. If the engine picks up smoothly then everything is good, but if the engine falters or refuses to rev from tick over, then turn the L screw slightly to rich (counter clockwise) and try again.
Sometimes a compromise needs to be made between the smoothest tick over and the best pick up.
These adjustments all assume that the carb is in perfect order and correctly set up. In particular the height of the needle valve arm, as if too high the mix will be rich and if too low it will be lean.
Also, ensure that you turn the screws very, very slowly and keep an awareness of the the screwdriver position at all times.
Hope this is understandable and that it it helps.