Grass trimmer maintain and repair

To start a cold engine:
1. Place the on/off switch in the ON position.
2. Slowly press the primer bulb seven times.
3. Rotate the choke dial clockwise to the FULL CHOKE position.
4. While squeezing both the trigger lock and throttle trigger, push in the throttle lock button.
Release the throttle trigger. This latches the trigger for starting.
5. Pull the starter grip sharply until engine attempts to run (no more than 4 pulls).
6. Rotate the choke dial to the counterclockwise HALF CHOKE position.
7. Pull the starter grip sharply until the engine runs.
8. Allow the engine to run for 10 seconds.
9. Rotate the choke dial counterclockwise to the RUN position.
10. Squeeze the trigger to disengage the throttle lock and return the engine to idle.

PREMIUM EXACT MIX (50:1) 1 gallon gas (US) / 2.6 oz oil, or 1 Liter gas /20 mL oil

Usage
You should change the gas/oil mixture and replace it with new stuff if you did not already do so. Insure the choke is set to full choke when you start a cold machine. Move the choke to full opened after the machine has warmed up. If you machine has a primer bulb, usually a small plastic type button, push it at least 8 times before you attempt to start it. Try a few pulls with choke on - then try a few with choke open, keep the throttle fully open and pull the starter cord. If it doesn't fire, spray a little starter fluid into the air inlet and repeat the above sequence. You can get the starter fluid spray at a 'box' store or auto parts store. If it starts, let it run for about 30 seconds and then gently release the throttle and and then adjust the choke to the off position, as they are very temperamental, and just need a bit of coaxing.

Repair
All these small 2 stroke engines are difficult to start if the fuel-air mix is not right and they are prone to over choking.

If the engine is not running, the cause can be poor spark, lack of fuel or air delivered to cylinder, or some sort of mechanical failure such as low compression. Check the easy stuff first, i.e. fresh fuel mix in tank; on/off switch on; air filter reasonably clean.

1. Check the fuel system to ensure it is ok and no blocked filters etc. Clean out the fuel tank and put some fresh fuel in it.
2. Air filters. Ensure they are clean and allow unrestricted airflow into the carb.
3. Spark Plugs. Take out the spark plug, clean and dry it, if you know the plug gap check that it's right, if you don't know the gap and it hasn't been altered leave it as it is, If the plug looks anything less than perfect replace it.
If the plug is wet with fuel, dry the plug and do a few pulls before reinstalling the plug (keep spark plug wire away from the open hole). Reinstall the spark plug and try the above again.
Check for spark by taking it out, putting it back in the boot and grounding the threads to the head and watch for a blue snap.
4. I will agree that clean plug and air filter are necessary for superior running condition. However, the two most common problems that I encounter in 2 cycle products is carboned up anti spark screens/exhaust ports and varnished up in tank fuel filters. If, after checking the above four items, try adjusting the high and low speed screws counter clowckwise half a turn if the carb has them. If adjustment doesn't help I rebuild the carb. If no adjustment screws are present, the diagphram pump in the carb is likely hard and not capable of pumping proper fuel.
5. If at any point in this process it fires but won't run - the carburetor is probably dirty/gummed up etc. This can be caused by using old fuel. If this is the case, spray some carb cleaner into the air intake after you removed the air filter.
6. If the above does not fix the problem adjust the jets in the carburettor. It is possible that with all this pollution stuff happening that the formulation of the fuel you are using has changed causing the unit to change tune.

Repeat above sequence.

change the plug and air cleaner don't use starting fluid in a two stroke engine their is no oil in it and you could cause piston/ring/cylinder damage.

http://forum.doityourself.com/showthread.php?t=270292
Seatech:
Hi, all. I'm looking for some help with my trimmer. I bought a Homelite String Trimmer (UT20699) at a garage sale ($5 woohoo!). The kicker is that it won't start. When I got it home, I noticed that the 2 fuel lines were out of the tank, so I got new lines and a new filter (I think I have them going to the right lines on the carb as there is fuel showing up in the primer bulb). But the trimmer won't start. It doesn't really sound like it's trying to catch. First I tried spraying a little starter fluid in the carb and then a little in the spark plug hole but it won't go. I checked the plug and it's all black on the tip (not sure if that counts as fouled or not). Also, I noticed that when I pull the throttle trigger the throttle on the carb isn't moving....seems to be stuck but I was able to movie with a screw driver. Anyway, I'm pretty much a complete newb when it comes to anything mechanical so any help or advice you can offer is definitely appreciated.

v8driver:
You need to buy a carb kit for that particular carb, tear the carb apart and soak it in carb cleaner and blow it out through any and all holes real good. Sounds like the throttle cable might be broken if you could move the butterfly on the carb with ease. And of course you could have a fouled spark plug but check for spark by taking it out, putting it back in the boot and grounding the threads to the head and watch for a blue snap. Nothing? remove the kill wire..... still nothing then a new coil...
Also you should check the cylinder and piston through either the spark plug hole or exhaust port for scoring.... any scoring, probabally will have too low of compression to even start, and a new cylinder, piston and rings will need to be bought... not really worth it either. A 2 cycle like a trimmer, under 90 psi of compression is bad, even at 90 it'll be hard to start, over is good.

Seatech:
Thanks for the response, V8.
To check for spark, when you say to ground the threads of the spark plug to the head, do you just run a wire from the threads to the engine block or to the tip of the spark plug? Also, after it's grounded properly I assume I just pull the cord and see if there is spark, right? Sorry, I'm really a complete novice when it comes to all of this, so sorry for my ignorance.
Also, I can move the butterfly but it doesn't move easily at all. When I pull the trigger, the cable does seem to be moving but the butterfly seems to be stuck, so I'm guessing it needs to be cleaned?

cheese:
It can be hard to ground a plug on some trimmers with all the plastic they have on them. Sometimes I wedge a screwdriver next to the cylinder, and lay the plug on it in such a way so that the metal on the plug is touching the metal on the screwdriver, and the screwdriver is touching metal on the engine. You can use your wire method too, or whatever it takes. Sounds like the carb does need cleaning.

Seatech:
I got it started!!!!! woohoo!
Ok, so after reading your tips on checking for spark, I went home after work and pulled the plug out and for the ground I cut the cord off an old charger for a cell phone I no longer have and taped the wire to the threads on the spark plug and then to the engine. I got spark, and it looked good and blue, so I put the plug back in and took the muffler off and cleaned the screen.

I put it all back together, closed the choke, completely and gave it 6 or 7 pulls on the cord. Switched the choke to the next step open and pulled again...and it started! (kinda scared me actually. lol)
So, thanks for all of your help. Gotta love the internet!

I do still have a problem with the throttle not moving by itself. It's basically stuck wide open. I can move it with a screw driver, but it's not easy at all. Any tips on getting that working besides liberal use of wd-40 or some other lubricant?

v8driver:
You still need to clean the carb..... sounds right now that the butterfly is stuck in place maybe by gummy gas. Or the shaft is broken on it and its rubbing (unlikely but possible).