Jon: I have been following your interesting thread on sealing the piston on your Rochester B carb and your creativity on trying to improve this design with new ideas. Several months ago I refurbed my Rochester B for my 235 and remembering looking closely at that piston in question so this peaked my interest. About 10 years ago in my profession I had to design a pneumatic valve with a similar spool piston that required extreme sensitivity( no seal drag) yet required good sealing. My first attempt was with O-rings but needed even less drag. I opted for using X-Rings (or Quad rings) that offer much less seal drag plus other benefits. These guys will fit into and existing O-ring seal gland. (I attached a catalog screen shot of the benefits). Possibly these rings may help in your endeavor! or Google it to learn more.
The downside is that they are usually in stock available only in the common Buna N ( Nitrile) compound which is not compatible with ethanol gasoline but possibly you can find some of the correct size in neoprene and other compounds which holds up with ethanol gas. They can be molded in any material but in large lot quantities which won't help here but stock may exist from overruns.
In addition, I have also used the Teflon rings in addition to the rubber seals to keep the seal compression the same on the installed diameter of the seal. The standard o ring design seal clearance between the piston and bore should be .001"/.0025" PER SIDE ,which I think is where you are.
Good luck with your determination and thinking outside the box. Remember necessity is the mother of invention. Where would we be without it!
