Generally you do that by gradually adjusting the idle mixture when
it's idling and the main when it's a full speed. With the needle
turned in too much or out too much it starts to run rough. About
half way between those two spots is where you want it. A little too
rich is better than too lean. .
The problem transitioning to full throttle can also be due to
else, leaking crank seals being one thing that causes erratic
First things first: service your air cleaner.
Now, a 2 cycle engine has three screws; two mixture screws (high and
low), and an idle speed screw. The idle speed screw does just what you
think it does, and the mixture screws set the mixture at WOT (high) and
at idle (low).
Since your machine has trouble getting up to speed, you will want to
play with the low mixture screw.
Before you get started, make sure you note where it is now, just so you
have a place to return to should things get funky.
So now that you have narrowed it down to only one screw, I usually like
to get a feel for how far the screw is turned out to get a reference
value. Turn it in all the way, being careful not to tighten it too much
at the bottom (you can damage the needle seat otherwise). Make a note
of how many turns it took.
Now turn it back out the same number of turns, plus a 1/4 turn. Start
the saw and play around with it, taking note of the performance. If it
shows no improvement, or is worse, repeat the procedure, but this time
subtract a 1/4 turn.
Guys who work with 2-cycle engines would know right of the bat whether
you need to turn it out or turn it in, but since I don't do this often
enough to "know" which way to go, I find the right setting empirically.
Anyway, that's how I do it. You can probably find a good video on
youtube that shows a guy actually doing it, which can be helpful. You
might also run into limiter caps on your machine, which are something
else fun to have to deal with.
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