Wont idle have to run on 1/2 choke

Make sure your fuel mix is fresh and of the right gas-oil ratio. Today's pump gas has Ethanol mixed with the gas and can go bad in as little as 30 days. this stuff is terrible to run in small 2 cycle engines. A lot of loggers I know buy Ethanol free gas for their saws. Also do not ever use starting fluid to start a 2 cycle engine ! What happens is the Either washes the cylinder wall of oil and now you have a scored piston and/or cylinder

Do you have too much oil in your gas?

Sounds like the carburetor needs a cleaning and rebuild. Make sure that you replace the diaphrams also while there.

I hope this is helpful for you.

If it only runs with choke on, then mixture is too lean or idle set to low.
Adjust mixture initially at 1.5 turns, then move in or out as needed for highest idle when warm.
Make sure no leaks or clogged filter when adjusting.

Hard to say with string feed, but are you sure you are not putting the spool in backwards?

Well, here is a user's manual (for your convenience).
http://lawnandgarden.manualsonline.com/mdownloads/0ccba814-582d-4529-9948-3997ee193ccc.pdf

Here is the parts breakdown with diagrams and prices of the closest trimmer to your model.
It is practically the same.
http://www.ereplacementparts.com/homelite-ut20043a-25cc-reach-string-trimmer-parts-c-18807_20299_20500.html

the problem is in the carburetor most likely, it may be cleaned and adjusted, if not it will likely need a new carb

http://docs.google.com/viewer?a=v&q=cache:gez_QotI2HkJ:ipl.ordertree.com/ipl/338/UT20004A_24A_44A_685_eng.pdf+homelite+trimlite+manuel&hl=en&gl=us&pid=bl&srcid=ADGEESjYoEmqbDTW9YxRajkdBOlyuM0QdOAJ_IaDGa1FZcpdF45MaCC9o7AuF2DQOWwV4jGh_C6iP7hzhTQkDreYz2qVBSNtcFiQIs0LdZoRQJi1cwSYGEnEV1H6NFkHwNUAl2axj1uy&sig=AHIEtbRXhjlqA0rUAC7zcHsMGLQzgOAJAw

Run some combustion chamber cleaner (not carb cleaner) through the carb with the air filter off.

Your main jet is partially clogged and it needs a richer air / fuel ratio to run - hence, why the choke needs to be all or partially on.

Hope this helps!
Rob

You need to disassemble the carb. and spray with carb. cleaner. If you need tips on how to do this, just let me know. You may need a new carb. kit as well, but we won't know that until you first perform the first step, or if the carb. parts are more than 3 years old. If they are, then go ahead and buy the carb. kit and replace the parts.

Jim

Check the muffler for obstructions. Remove the muffler and check the exhaust port sometimes they are near plugged. If so remove all the crud with the cylinder in up position to prevent getting carbon in cylinder. Trimm to adjust Turn both L and H set screws clockwise until they bottom the back each one out 1 and 1/4 turn. This should allow you to start the trimmer. Then rev to max rpm and adj. the H screw to max rpm. Then set the idle with the L screw with good idle without string head turning. Then when throttled it should do so without hesitation. Once this is set you may have to fine trim the H screw for max rpm again.