Small Engines (Lawn Mowers, etc.): Engine dies after 10 - 15 seconds, fuel system components, c1q

Question
QUESTION: I have a Stihl FS55R string trimmer that starts and dies after 10 - 15 seconds. I used it in early September 2009 and when I went to use it again in October I couldn't get it to stay running for longer than 15 seconds.  I replaced the fuel filter, checked the exhaust port for blockage, wire brushed the spark arrestor screen and rebuilt the carburetor with no improvement. One item though, when I was rebuilding the carburetor, the instructions talked about a welch plug. There was a replacement welch plug in the kit, but I found no welch plug on the carburetor (C1Q type). Should all carburetors have a welch plug? Any other suggestions for getting the trimmer running? The trimmer is not that old, around 5 years. If I have to buy a new one, any suggestions on a reliable brand?  

Thank you,

Frank

ANSWER: It sounds as if you have a fuel delivery problem to the carb. Check all fuel system components before it gets to the carb for proper seals and no holes in the lines. If your are good there, then the issue is most likely in the carb. I have found that trash gets stuck behind the inlet screen for the inlet needle to cause this issue.
Recheck your carb build once more. If your still have the same issues, replace the carb, it will be much cheaper then replacing that unit.

---------- FOLLOW-UP ----------

QUESTION: John,

I replaced the lines from the tank to the carb and I was able to start the trimmer and keep it running for as long as I kept my finger on the throttle. So thanks, that got me to the next level. With the throttle trigger pushed in all the way the engine never gets to what I think should be the maximum speed. It also runs very rough (almost like it's missing) and stalls when I remove my finger from the trigger. I had already replaced the inlet screen when I rebuilt the carb.  I replaced the plug, but it didn't help. I tried tweaking the carb, but that didn't help either. Although I have used older fuel in the past, the 50:1 mixture I used is about 4 months old. Is my next step replacing the carb?

Thanks again for your help.

Frank

Answer
Yes replacing the carb seems like the most logical next step. My advise on this is to get all the numbers off the carb and go to a big dealer that is not stihl. The stihl dealer will charge extra most likely, because of the stihl name brand. This Zama carb can be ordered by a Zama dealer. ALso once you have replaced the carb,try to find a gas station in town that doesn't have ethonal in there fuel.