Holley 80457SA 600 CFM carburetor. The car is a 1964 Nova with 250 inline 6 cylinder. The issue is most noticeable when cruising with the throttle barely open. The air/fuel ratio goes over 17:1. This engine doesn’t like anything much over 15:1, so it surges & loses power until the accelerator pump is activated by accelerating. It idles at 1000/800 in gear and 13:1 AFR. The surge doesn’t seem to improve with changes to the idle screws or primary jets. Power valve is an 8.5". Are there fixed jets I can drill out to increase fuel just off idle?