I am trying to track down a misfire/strange idle on my 1971 Charger/440.

It is idling along a 900 rpm in Park, then it will idle up to 1,200 for a few seconds, then idle back down, and then repeat. It's annoying as anything. It starts to do it pretty much as soon as I start it, it doesn't only happen warm or cold.

One thing I noticed while adjusting the floats is that when I loosen the adjustment screw on the primary side (engine off) to raise or lower the float level, gas leaks out, but it does not do this on the secondary side. I thought maybe the needle was sticking or something, so I put a brand new needle/seat assembly in, it made no difference to the idle.

Is it possible the primary side is getting overpressurized or something and dumping fuel until the pressure drops? It's a Carter mech fuel pump with a QFT carb. The float levels appear to be spot on at idle

Any other ideas what would cause that type of idle issue? I am pretty sure there are no vacuum leaks, but maybe I am missing something along those lines. I also made sure all my plug wires are isolated and I am not (I hope) getting a crossfiring thing happening.

All help is appreciated.

Greg