First of all, daily drivers are going to have much less trouble with the power piston sticking. It isn't those situations I'm addressing. It is the people who start their engine once a month...those are the people who are going to have the headaches. Their power pistons are in time going to be stuck and "varying load conditions" will have zero effect on anything happening in the carburetor at that point.
There are at least a couple of ways to approach the power piston problem in my mind (and ideally this needs to be something included in a rebuild kit):
1. Devise a way to block any gas from entering the piston and bore. Today's gas is going to guarantee this piston sticks when it evaporates. That is a given for occasional use engines. And I've come up with ideas. Here is one:
http://i1154.photobucket.com/albums/p535/JonGoodman/Aluminum%20frames.jpganother view:
http://i1154.photobucket.com/albums/p535/JonGoodman/Rochester%20seal%20idea.jpgThe aluminum frame I've made holds something around the piston which seals and keeps it dry and this frame is held in place by the mast. Could be an o-ring, could be a piece of thin neoprene, a nylon ring or could be a leather ring. I haven't found the best way to seal it yet, plus the air horn to bowl gasket would have to be modified. I think the best answer might be an accordion-like seal that would fit on the power valve rod and be held tight at the piston bore but holy cow that little seal would cost a fortune.
Another possibility is to make a power valve that sits outside the carb and run the rod down to the power valve. But there are plenty of challenges there. One for example:
what strength for the spring? It won't be the same for all B and BC carbs (I found 3 different spring tensions in just the 5 that I studied). Plus that would not be something you could include in a carb kit.
2. Devise a way to keep the piston from being in constant contact with the bore and seal it a bit in the process so any gas that reaches it will only affect the bottom 2mm of the piston. That's easy and cheap. O-rings. As you pointed out there are some limitations. The maker of these says they're tolerant of gas, oil and even ethanol. How long will they last? I don't know yet, but I'll find out. But I do know the design of these carburetors and the gas being put into them suggests to me occasional use carburetors are going to work best if they're serviced at least once a year. I've thought also of split rings (ptfe coated, nylon, pvc, delrin, etc) and I think those would work but again we're looking at $$. I haven't yet found any existing (as stock) items.
If you have any suggestions, please put them out there.
