You may have rear gears for a lugger like 4.88s, the cam could be retarded or a top end grind (not officiant till high rpm), you may not have enough initial or total advance. starting at the carb. to save gas is not where I would start. did you install the 1.7 ratio rockers? can you put a dial indicator on the heal of the rocker (at the push rod) and give us the lift of the cam lobes I&E? How many miles on this engine since you assembled and started it? Is it a roller or flat tapit ? If its an automatic does it have a stall converter?