Here are some of my Rochester B thoughts from the last 44 years......
One of the biggest problems with the Rochester B is actually the manifold gasket included in most of the rebuild kits. The B uses a vacuum signal from the manifold to lift the plunger on the enrichening circuit. Many of the rebuild kits use a gasket that does not have the hole open for the enrichening circuit - hence you drive around super rich all the time.
Second problem with the Rochester B is that the brass enrichening plunger gets stuck in its bore and cannot be moved by the vacuum signal - you simply need to clean it up without creating too much clearance. The opposite issue is simply have the bore/plunger worn excessively. Pretty easy job to turn a new one on a lathe, especially if you simply counter bore and press a dowel in for the pin that contacts the spring loaded ball in the enrichening circuit.
Next issue is the worn butterfly valve shaft holes. Readily apparent when you cannot set idle mix correctly. Drill and bush is the easiest repair.
Another issue is tightening down the lid mount screws too much and warping the mounting ears. Original gaskets used an impregnated paper that did not weep gas. All the rebuild kits I've seen use a simple paper gasket that readily weeps gas. I have had good luck milling the ears flat and being very careful when setting the float level and not over tightening the mounting screws. I've also dropped the fuel level on one carb between 1/8 and 3/16" and then advanced the timing an additional 4 degrees to compensate for the slower burning lean mixture - this worked out really well with no weeping from carb.
Final thing is that some Rochester B variants have a check valve built into the body for the throttle pump - they require a throttle pump piston that does not have a built in check valve. Others do not have a check valve in the body and require a throttle pump piston that has one built in. Worked on several cars with severe off idle stumble and found mismatched throttle pump pistons. Somewhere in their lifetime someone changed the pump arm to accommodate the wrong pump piston.
