I've got a problem with my trimmer I need help with. It was fine one minute and then I don't know what happened. Now it either lets too much line and wraps around the shaft ,or it won't let any out. Then I have to shut it down ,pop the head off and let some line out. I bought an extra spool to make changes quicker so I checked to see if I was putting the line on correctly ,and I'm putting the line on just like the new one was. So what gives ,I had to stop several times on a job to fix this thing. I'm not bumping it to let line out it just comes out. Thanks for the help. It's a Stihl FS55.