Mothertrucker - Had Rochester only used 8 screws instead of 4 to hold the airhorn/bowl cover to the bowl on the B series carburetors, this would not be a problem. As they didn't, warpage from heating/cooling cycles causes an internal vacuum leak in the passage controlling the power valve, causing it to stay in the open position (too rich).
Double gaskets MAY work for awhile, but will hasten better repairs.
The procedure we use is very time-consuming, but also very simple and I will post here for do-it-yourselfers.
First obtain some scrap iron plate at least 3/8 inch thick. Drill holes in the plate to align with the airhorn/bowl screws; also machine the plate so that it can be placed flat on either the bowl or the air horn (or use two plates).
Now, screw the airhorn to the plate (snug, but do not tightened. With a feeler guage, measure the clearance between the airhorn and the plate. Take another plate and place on top of the airhorn; and using a rather sophisticated fixture (C-clamp), clamp the two plates together, squeezing the airhorn. Tighten the C-clamp to remove 0.003 inches; NO MORE. Set the assembly in an oven and heat to 400 degrees F. Allow to cool naturally. When cool, the C-Clamp will probably be loose. The heat and tension reverse the warpage process. Repeat until warpage is gone. Repeat for the bowl.
Of course, in another 15 years, the problem will return.
Filing or milling the castings flat obviously removes metal, and the repair will be very temporary, and ruins the castings for proper repair. Best to take the time and do it right the first time.
Oh, one other thing, best to NOT use the oven belonging to your significant other!
Jon.
