im useing an hei dist with drag racing springs.i do not use a vaccume advance.im certion the timing is right on.i rebuilt the carb only for the fact it was dirty and i like my stuff nice.as far as powervalves i assume your talking about metering rods and springs?it is an eddy.i reused the same springs and rods for they were in perfect shape.the only thing i changed were gaskets and pump shot spring which was alittle stiffer than the old one.im still not certian that a vaccume leak on the manifold would cause this,could it be my flotes depleting and not filling fast enough?im running at about 6 to 7 psi with a mechanical pump.thanks