My JD/Echo 21S string trimmer is acting up. I can start out and use it for one yard. It cranks and runs fine. Then the next yard the it won't do anything. Put a new plug in and it's fine for another yard. The plug looks fine when I take it out, not burnt or oily residue. I was told that I need a new coil, by the echo repair man guessing. A coil is around $75 and plus labor and this doesn't include diagnosing the problem. I wonder if I might be better off to just go ahead and invest in a new one since it is 6 years old.