Clunk sound when starting

due to the feeding issues with my new trimmer stihl fs55r, i am going to try some new line. i have found that there are many different kinds. not completely round and have some sharp'ish edges. i bought some line that is shaped like this cutter .095 [url]http://www.homedepot.com/catalog/productImages/400/dc/dc83d812-57fc-49b0-bb2d-084faa8c95e9_400.jpg[/url] seems too me that this line would be a fine cutter. if it doesn't cause some kind of issue/s but idk, that is why i am asking.

I have 3 partner concrete saws I bought not running. My plan was to fix them and sell 2 and keep one. Anyways about a year ago when I bought them I couldnt get spark on any of them. Sometimes it would have spark and most of the time they wouldnt. I was away from home for a while and just got back so I started to dink around with them again. I reset the gap between the flywheel and the coil and it had great spark. I put it together and it had spark, fuel and compression but wouldnt even fire once. I checked the spark again and nothing. Is it common for these ignition coils to fail like this where they make a spark and then dont work? It drives me nuts and wears my arm out. I have the wire pulled off to the coil that goes to ground so I know thats not the problem.