there are many good videos explaining it on youtube. its easier to see what people are talking about then just reading it. your instruction manual normally had it in there too.
however i will run you through the basics, which may change a little for different makes or models.
1. warm the engine up to operating temperature.
2. turn the unit off and turn each of the high and low screws until they 'bottom out' (make light resistance). STOP HERE AND DONT OVER TIGHTEN THEM AS IT WILL DESTROY THE NEEDLE TIP AND SEAT).
3.turn the screws out 1.25 (1 and 1/4 in old terms)turns.
restart the unit and try to accelerate. if the unit stumbles then try winding the low and high screw either 1/4 a turn in or out and see which way improves it.
4. make sure the unit will idle smoothly when the throttle is released. if it doesn't try adjusting the low screw in or out 1/4 a turn and see what way improves it.
5. make sure when the unit is idling the clutch (if fitted) disengages the trimmer head. if it isn't then turn the idle screw out a little to lower idle speed.
6. now the idle is set make sure the engine accelerates freely and doesn't stumble. turn the high screw in until the unit 'peaks' (revs at it absolute max, then wind the screw out a little to retard this peak. this is because 2 strokes shouldn't run at there absolute maximum rpm's because it is very hard and destructive on them.
this is my procedure and has always worked for me. if it doesn't then i may be wrong or you may have a dirty carby which is a different matter. i among many others have written posts on cleaning them before so a search will unveil many different procedures.
for the first adjustment before starting the unit sometimes you may need to turn the screws out 1.5 turns depending on the make model and engine displacement to make it run enough to warm it up.
good luck
regards jay
