Dual Quad 428 CJ

[Khobra]

Originally Posted by DanEC

The following may be a wild goose hunt as possibly I'm taking your comment out of context, but if your throttle plates are nearly closed you don't need to drill holes in your primary plates. Usually that was done on engines with a big cam and low vacuum because the primary throttle plate had to be opened excessively to get the engine to idle and they end up above the idle transfer slots in the bores - basically taking the idle mixture adjustment circuit out of commission.

You seem to have the opposite condition for some reason (throttle plate possible closed too far). Also, although I have drilled the throttle plate on one Holley before - it was before I discovered that most if not all 4-bbl Holleys have an adjustment screw on the secondary throttle plates. You have to pretty much remove the carb to access it because it's on the underside of the base plate. It's there for two reasons - first, to slightly crack the throttle blades open so they don't become wedged in the bores and won't open, and two, on engines with big cams and low vacuum the secondary throttle plates can be opened slightly more to pass more air at idle, allowing the primary throttle blades to be closed to where they rest in the middle of the idle transfer slots and the idle mixture screws will again function.

If you have a pretty healthy cam and your primary plates in the carbs are excessively closed you might experiment with increasing your idle speed or pulling the carbs and see if the rear secondary plates need to be closed slightly.

Dan,

I will start from scatch to make sure that all your points have been addressed. I may have made some mistakes. Will update you when I have conclusive results'