On 04/21/2013 04:58 AM, Frank Thompson wrote:
How can I determine if my 2 cycle string trimmer's carb setting is too
rich or too lean. Runs smooth idling and wide open. In trying to go
from idling to wide open it cuts off.

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.

Jon