Fitted the new valve, new spring, and new hammer that I bought on PCP tunes advice for the mk1 stealth. £160 later fitted but rifle started to fire on it's own. I took it to a specialist, who checked what I had bought. The hammer was 10g lighter than what it was advertised and longer than it should of been which was the reason the gun was going off on it's own. , the spring was weak, but the valve was ok. The rifle is now bang on and running 35 foot pound. A new stronger spring and hammer fitted.
I am now very happy !!
Not christened it yet but I'll let you know what I find out in the field.