I've got a completely unexpected situation, but this is information which may be important to you and should be checked if you're rebuilding a YF. A YF3211s of mine was running very rich. This is the same carburetor I mentioned a few weeks ago was missing the vacuum bleed hole. I thought at first that was the whole problem, however it turns out the missing bleed hole was only a secondary problem. The primary problem was warpage of the pump/diaphragm housing and this was the first time I had ever seen it. However I think there's a chance it might be more common, hence this post.
There are 4 screws holding the housing in place and overtightening of these can cause the housing to warp. When this happens, the vacuum that is always present at the bottom of the diaphragm will suck gas out of the float bowl, underneath the diaphragm and straight into the intake manifold. For a couple of reasons, this will make your YF operate poorly...and it certainly isn't limited to the 3211s at all. Let's take a look. The first four images below show some of the YF housings (or bonnets). One is an older type which is flat on the bottom, one is a newer type which has a raised ring on the bottom and the other is another older type which incorporates a couple of jets and a spring-loaded check ball. Then the final image shows the diaphragm well and the vacuum hole at the bottom of that well (at about the 11 o'clock position). On to the next post due to image limitations...
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
