I'll have 50p on something not being quite right on the power valve side of things, how to set it all up is about 3/4's the way down this page.

But first of all, check the power valve butterflys (they're these things, there's one on each barrel) aren't loose on their spindles.
The thread on the spindle is left handed (i.e. tighten it anti-clockwise).
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