You can get at the clutch - it sounds like you may have some slippy stuff in there - but that wouldn't explain why the drive comes back ...

Anyway - to get it apart is basically just a stripdown - there are 3 bolts holding the leg on and then 4 holding the bottom engine cowling on - you'll have to take the top off and I take the fuel tank out as well. You'll also need to take the tiller arm off and the kill/stop button off ...

If you're careful you can get the clutch housing off the bottom (the centrifugal part is on the bottom of the engine) without removing the exhaust ....

One blummin good clean later and you can put it all back again .... I've done ours a couple of times (once per season) and although it is quite tedious, I find the engine to be reasonably reliable and the Centrifugal clutch is excellent