Hi everyone i hope someone can help me.

Ive been given a ryobi 705R trimmer with a speed spool head.
I have no problem in winding up the line but once its running the line just shoots out again. Ive tried installing it tighter and cleaning up the head assembly but its still the same.
I also noticed a crack in the slider assembly so thought that was flexing, i welded it up but still the same. Im now wondering if the springs on the slider are strong enough?
Anyone else had this problem?

Matt.