I have a Ryobi touch-start. When I started it at the weekend, it started fine, but the head turned then stopped or didn't turn at all. It's under warranty but the nearest service centre is the other side of Leeds, so if anyone can tell me whether it's something that I can fix myself, I'd be grateful.
There is a centrifugal clutch in strimmers, the faster the engine revs the better the grip. If you have been just pottering with it the clutch strips and wears out quickly. But the splines on the shaft can wear as well if you are working it too hard. Ryobi spares should be easy to get and if you are good with spanners, more of an expense than a problem. There are a few spares on ebay at the moment.
How to remove a strimmer clutch somewhere on this page if you scroll down
http://www.ereplacementparts.com/ryobi-ry29550-string-trimmer-parts-c-7931_15633_15647.html (http://www.ereplacementparts.com/ryobi-ry29550-string-trimmer-parts-c-7931_15633_15647.html)
check the shaft to the engine and head,somtimes they move a little and don't connect to the drive.loosen them and shove them together.