Right here's the adjustment procedure for the mechanism after removing the sprocket cover.
As Duncan says better to buy a new one rather than clean insides of the old one.
However, before you buy a new one, do this. Take the sprocket cover off, give the whole area behind a really good clean. Remove the mechanism, clean the outside, remove the push rod and give that a good clean too.
Put it all back together and adjust as per the manual says, if it doesn't help, then buy a new mechanism, thats after checking chain tension & making sure your oil level isn't too high
sv clutch by
maviczap, on Flickr