Timing Jumping Around

New 440 build, new timing set, distributor/oil pump gear, distributor (Firecore), ECU (4 seconds flat). When I check the timing, the timing mark jumps all around from retarded to advanced and then will settle on the "0" mark for a second or two. I can hear the engine sound like it's surging a bit while its doing that, idle speed going up a little, then back down.

Not sure where to go with troubleshooting this.