Dusty, you need to adjust the metering rod. It sounds like you are running way lean. The rod coming off the throttle shaft runs up the back side of the carb and works the accelerator pump and metering rod. There is a tool for setting proper depth, but in your case not much help since the engine is not stock. To set mine, I used a dial caliper and measured the hight of the metering rod as it sets at idle. I measured from the small shaft the rod slips over to the base of the top, the dial caliper was used like a depth gauge. I then raised the metering rod, bending the long rod at the base where it makes the 90 degree bend, .040" and went for a drive. I kept raising the metering rod till the flat spot went away, it took three test drives till I was happy with it. Fuel milage will suffer if you keep raising it, so stop when it feels right, you can always go back the other way. If by chance you can't get there, you may need to open up the jet or change to a richer metering, rod.
http://quadrajetparts.com/carter-ca...r-parts-metering-rods-c-299_312_395.html http://old-carburetors.com/Chevy/pages/001-Chevy.htm, this link has the original Carter files, go to the home button at the top left to find your carburetor if its listed. Under the parts section it will list the OEM part number of the metering rod and jets. I use these numbers to search e-bay for what I want.
Joe
