The early metering heads have a blancking screw on the idel CO adjust, which needs to be on or it's an air leak.

Now the later doesn't need a scew, it seals itself. But, is there an anti tamper screw/cap above the actual adjustemnt scew? Mine has never had one, but i think they do as std?

 

I remember there being an anti tamper plug on some of them Rick. One of the directors at work had a Series 2 and that had one.

 

this one looks like someone's had a go with the wrong sized key, and i cant get at the CO adj.

 

Just take it off teh head and do it as per an S1.

 

Thats the plan Butchers