I know this is not a chainsaw but figured they are similar (being 2 stroke). I recently picked up a used stihl fs 55 rc weed eater. I changed the spark plug and it would start but smoke a bit. There was a bit of oil on it. I figured maybe the fuel mix had too much oil so I emptied it out, pumped the primer until it was empty, then ran it for a few seconds. I put fresh fuel in from my container and now it wont start. I know it is not my fuel since it works in my troy bilt weed eater. I have tried using starter fluid and still nothing. It doesnt make sense to me that it would run one second, then not fire at all the next. It is getting fuel. I havent checked for spark but I dont see why it wouldnt be sparking after a couple seconds of changing out fuel. It seems the fuel mixture would be the issue but like like I said, it works just fine for my other weed eater. Any suggestions?