A few years ago (while doing the work on straightening the Rochester B carburetors) I set out to find anything else that may have been warped or not flat and I discovered the bonnet piece that sits atop the diaphragm in the YF can be warped. If this is the case (and the one I used for the example was warped by .008" on one side and .006" on the adjacent side) what happens is the ever-present vacuum that regulates the diaphragm/metering rod assembly will suck raw fuel right into the manifold. In other words, the chamber loses the air-tight nature it needs to work and two things happen: 1---there isn't enough vacuum to hold the metering rod down so it moves upward into the area where it allows more fuel through the main jet and 2---it sucks fuel through and into the engine. Makes for a rich situation. There was a gasket developed to help remedy this but Jon H doesn't use it, feels it worsens the situation and I agree.
So using a flat piece of wood and some sandpaper I "machined" the casting to correct this. Some of the images of what I did below.
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
