McCulloch TrimMac 250 Strimmer starter?

My strimmer starter cord will not re-wind automatically. It will when I manually wind the strimmer head in the opposite direction to its normal travel. I'd like to dismantle it to see what has broken/jammed, but it was not obvious what was going to happen when I took out the four coarse-threaded screws which hold the handle/throttle lever/ignition switch and the upper plastic sleeve on the drive shaft. It felt as if it wanted to fall apart, so I did it up again!