Good show! You will find that a tired Carter carburetor is several steps of improvement over a brand new Rochester B. Someone did you a huge favor by swapping carbs sometime in the past. "The ABC's of carburetion- - - -Always Buy Carter!" That was Carter's slogan back in the late 1940's and early 50's!
Just draining the gas tank might not be sufficient. When you add fresh gas, it's going to dissolve the gummy residue that's left, and it will end up in the valve guides. Either remove the tank and have it professionally cleaned, or replace it. My tank-cleaning method involves putting a couple of shovels full of fine gravel into it, strapping it to a rear wheel of my tractor and mowing a few acres of pasture. The only tricky part is getting the gravel back out!
Jerry
