This product is simply awesome! You can adjust and control the opening speed of your EC250 or EC300 powervalve... Wayne Braybrook used one when he won HELLS GATE when the conditions are very extreme and Trials like where a very flat, trials kind of power is needed. You can turn the knob fully anti-clockwise to stop the pv opening fully, or clockwise to even speed it up more than standard! All in all a very good product that makes a massive difference to the bikes performance. NEEDS GOOD MECHANICAL SKILLS FOR FITMENT!