I have a 550e silver series walk behind mower that i purchased at sears last summer. It was great. Primed the cold mower for a first pull start. Then a first pull start without priming every time thereafter when I would shut it down to empty a bag or something (warm engine start). Well I didn't store it properly through winter and it wouldn't start this season. I took it to the Sears service center and that changed the spark plug with a RC12YC spark plug which is not what the manual lists. Is this a correct option? They also said that the problem was that the carb. needle needed adjusting. They did these two things and I picked it up from service when they called me two weeks later. So I go home and test it out. First I primed 3 times as per instructions and it took a couple of pulls to start. I used it for a few minutes and shut it down. Then I tried to start it again and nearly pulled my arm off! Nothing... So I primed again, and it started. Tried a warm start again and it took about 6 or 7 very laborious pulls to get it started. Seems not to want to start unless primed. Any suggestions as to the problem? I'm going to bring it back to Sears but I would like to have an idea as to what they should do because apparently they don't know.