Demon 850, came with a power valve, but it never has run right for me. I've been inside this thing many times, and only have it on the car for short periods of time (keep putting the Holley 750 back on) After the last time of messing with it, it idles good, goes down the track ok, but there is an off-idle problem. It idles great, but if you bring the RPM up around 1600-1800 there is a flutter/stumble. If you go past that point, it clears up, below that point is good too. Does the same one my 302, so I know it's not an engine problem. Could that be a power valve problem? Or an idle transfer problem? I blocked the power valve off when I first bought it, chasing poor running conditions, but on this last time, I put it back in. in the beginning, I borrowed the EGT off the Jr Dragster and I never could get the temps as hot as with the Holley, that's why I pulled the PV out, changed the jets, and got it close, but I just put my 750 back on. Most opinions are to sell it, some have good luck with them, some are junk out of the box. This one was bought more than 10 years ago.