How do I get the diaphragms back in correctly?
As years go by, and as you pull and disassemble your carbs a few times, the diaphragms of the jet needle vacuum pistons (usually just called 'diaphragms') may start to become a little misshapen. Not a big deal, but reseating them could become more of a chore each time.
One problem could be that the diaphragms get kinked and out of round under the top boots. Unless they are torn, you don't want to replace them; new ones are over a hundred bucks. To get them back inside the carbs, there are a couple things you can try.
The first is to get them cold, so they shrink enough to be put in correctly. Put them in the freezer for a couple hours. This should make them shrink a little and stiffen up enough to get the rubber rims lined up with the groove on the carb body.
Another help is to get three sides in. Then, the tongue sticking out of the last side will protrude about 1/4". Cut a scallop in a piece of thick cardboard, roughly the same radius as the outer rim of the diaphragm. With this, gently push the protruding edge of the diaphragm roughly into place, doing final adjustment with a small screwdriver. Do not tear the diaphragms. Maintain just enough pressure on the cap to retain the already seated part of the diaphragm (using hand and screws). As a last check, slacken the screws a bit and wiggle the cap around in the hope that this will allow the compression around the edge of the rubber to even out somewhat.