I'm sorry if this has already been asked, but I don't even know what to search on, and it's my first time here.

I have a 2-3 year old, straight shaft Troy-Bilt string trimmer / brush cutter, that has been running perfectly until a couple of weeks ago. It used to start on 1st or 2nd pull, but while I was using it one day, the engine started running slower, and when I opened the throttle up, it choked and cut out on me. It was very hard to start after that, and now, when it's cold, I have to pull the starter 20-30 times (at least) in order to get it to run at all. The, if I don't let it idle for 3-5 minutes, if I pull on the throttle, it'll cut out on me. Once I do let it warm up, it's still slow to accelerate when I pull the throttle and will not run at full speed. When running it with the throttle wide open, it sounds like it's sputtering or backfiring on a very frequent basis (a few times per second).

I checked and cleaned the plug. I checked the fuel flow, tried running it w/o the air cleaner, I even completely disassembled and reassembled the carb, and everything seems to be in perfect condition, including the main fuel jet.

I've never worked on a 4-cycle before, and 2-cycles have not given me this kind of problem that wasn't easily fixed by cleaning. I honestly don't know if it's even a 4-cycle issue or not, but I'm drawing a blank on what to look for next.

If anyone has any ideas what I might be able to check or do to get it running normally, I'd really appreciate it.

Thanks.

-John

Well I am not the best weedeater mechanic,frankly hate to work on the darned things,but sounds like maybe you have carbon buildup in the exhaust port, or spark arrestor screen, you would be suprised how a little backpressure on these things can affect their running.Make sure your exhaust is clear.

http://www.smallenginetrblshtng.com/sitemap.html

i would try a new spark plug if its fouled just cleaning it wont fix it when a plug fouls out it is up inside the threaded end where it jumps fire so cleaning it wont do anything unless carbon is built up and closing the plug gap off ,,, does it have a bail up on the handle that kills it when its let go ? if yes then look down where the cable hooks to the flywheel brake there will be a small tab that slides back and forth and comes in contact with a rounded small wire . check it there and make sure its not touching with the bail up (run position ) if its too close vibration will make it short the coil out and make it do what it is doing

the valves could be out of adjustment

Is this the 4 cycle engine or the 2 cycle?

I have a Craftsman string trimmer which I have to clean the exhaust carbon out at least once each summer of use because of the exact same symtoms you described. Clean the carbon out of the muffler and screen and you should be fine.

If thats the case, try running some marvel mystery oil in the gas, and clean the carbon once more..... see if it helps.