Thanks heaps Toobs. I found what I think you were talking about (sitting in car left hand side, is that it? That's where I found it anyway). Mine had a screw type adjuster on the top. All I had to do was unscrew it a bit to allow a greater vacuum in the pick up tube and the revs went up. I don't know if yours has the same system...but does that sound like the part you were talking about?
I can hear quite a bit of air around now since I opened that valve up a bit , do you think that is normal. Couldn't really find leak in line.