2 cycle too lean vs too rich fuel symptoms

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.
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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 valve 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 something else, leaking crank seals being one thing that causes erratic performance like that.
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On 04/21/2013 04:58 AM, Frank Thompson wrote:

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
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On Sun, 21 Apr 2013 04:58:08 -0700 (PDT), Frank Thompson

Sounds like the idle mixture is too weak. (lean) I'd richen the idle mix a quarter turn and see what happens.
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