My new 80555C idles best with the screws out only 1/2 turn, Holley said I may need smaller jets and my vacuum is borderline for the PV. I went from 64's to 60's and changed the power valve from the 6.5 to a 5.5. The idle speed went up about 250-300 rpm and the plugs got whiter. I turned the idle stop screw out to slow it down to 1000 and 750 rpm in gear. Still the screws are best at 1/2 turn out. I think I need a couple of new plugs again to better read them. Just how fast do the plugs give a good reading when driving? For a primary check can I just go up my steep 1/10 mile driveway at 30+ mph.

I'm sort of thinking there is something wrong with this carb, it came from the factory with the idle screws out only 1/8 turn! The first tech I talked to said it was probably out of the box and someone messed with it, but I don't think so, it was perfectly packed. The 2nd tech (above) really sounded surprised at only 1/2 turn out. This is on a mild 454 so could it just be the greater airflow is making the venturis work better?