I tried one on a B pipe and it blew, so I trashed it (actually sold it). I don't think "in theory" they work like people think they do. First off, your waterbox never dries out, even if you run the valve. Second, if your motor's running, the waterbox never fills up with water. 3rd, reducing back pressure is ass-backwards to 2-stroke operating theory. Less back pressure means there is less force to return the unburned fuel charge back into the cylinders where it should be when the exhaust ports close. So with less back pressure you're burning less gas, which means less power.
I think if the valve works for you, you might be too rich on your jetting. And having less back pressure means you have a leaner charge left in your cylinder, so it'll burn better, making you think you got rid of a hesitation that was just bad jetting. You're wasting gas and making less power.
I'll stick by this theory until someone posts something that makes better sense (which nobody has done yet). Assuming that back pressure is bad is a very very wrong assumption. The whole point of the water screws is to add backpressure... the top screw adds the most backpressure and you'll find that the top screw gives you the best bottom end. Hmmm, funny how that works :27:
I have no dobut people can get the valve to work for them, but it's completely unnecessary IMHO. Anyone here ride my X-jet at Freestylefest? I ran a crapload of water into my waterbox (I tried many drier settings and decided on the "wettest" one was the best). I had one unrestricted stream going into the chamber stinger and one lesser stream going into the back side of the waterbox (it was a TDR box). TDR boxes are less restrictive than OEM boxes, but I ran about twice as much water into it as you would into an OEM box. And that made the best power, with no hesitation even after prolonged idling.