Before rebuilding one, check for play or evidence of leaks in the throttle shaft where it sticks through the baseplate. It is very common for Carter BBDs to wear out the baseplate and it must be drilled and bushings installed to get it back in spec. If the baseplate is worn, you might as well replace it unless you have the facilities to install the bushings. Also, look carefully at any replacement BBD you would get at a parts store for the same problem. Many of the rebuilders do not replace the bushings and instead install oversized plastic seals that wear out quickly. If the baseplate is worn, you will have fuel leaks onto the intake and a vacuum leak that will fluctuate wildly and can be impossible to track down and solve later on. I've had good luck getting decent rebuilt carbs from NAPA.