Hmm, I have tinkered with these regs before, and have one set to below 400 psi. I got it down there by removing a couple of washers. I use it on my Spyder VS2. I just had it out for the first time a few weeks ago and it kept up nicely with some quick short strings. Have you tried replacing any orings in it? Its been a while since I completely tore one down. Any internal scoring?