The Stovebolt Site Forums The Shop Area Engine Shop Rochester B -- what edition? and other Qs

Here are a few thoughts for you: the Rochester B was designed when real gasoline was used. If that isn't understood and appreciated, I believe it is likely nothing good can come from a Rochester B study. Real gasoline could be left in a can or tank for a much longer time and still be usable because deposits take much longer to form. And (the important part) leaded gas re-introduced to the carburetor will in time dissolve any deposits left whereas unleaded gas won't. Unleaded gas (even if it has no ethanol) will begin to get gummy after a few weeks. A friend (a retired petroleum engineer) told me this is because the "light" components evaporate very rapidly (and naturally evaporate first) and leave the "heavy" components which according to him quickly start becoming varnish which will not be dissolved with unleaded gasoline because fundamentally while you are waiting for the gum to be dissolved the "new" unleaded gas is rapidly deteriorating in the same fashion. So you're chasing your tail. His suggestion was "if you're going to use it, don't wait at all." He further said there is no reason whatever to leave an air space in your gas tank if you are not driving your vehicle regularly. He said ethanol gas can begin going bad in as few as 10 days (especially in the summer). Ethanol by the way is added at the time the gas is being distributed...as close to the time of sale as is possible. For good reason. While doing all the work on the Rochester B I took three vials of unleaded ethanol gas (each bought apx 1 week apart) and watched them. They were stored with the lids closed but with a space of air above them of about 2 or 3 inches. Every one of them started changing color in a few days. You can see them down below. In a month or so the first one i bought when poured into a metal cup and lit burned with a very heavy black smoke and left a gummy and tarry deposit.

So what is my point? Simply this: The power piston (in my opinion one of a few different Achille's Heels of the Rochester B) is doomed to get stuck and if the truck isn't used pretty frequently it could be only a couple of weeks of inactivity before it begins sticking. Of the five carburetors I broke down and studied, four had seriously stuck power pistons. They would not move at all. One didn't and it was because it had been sold as rebuilt by Autoline several years prior and had never been used. It had been wrapped in bubble wrap and left in a closet. I should mention the castings were warped but the exterior looked good. Every single power piston gets stuck in the "DOWN" position (meaning the carburetor is doomed to run as rich as possible at that point). I should add I tried every possible thing I could think of to keep the power piston dry. I tried making a rubber nipple, I installed viton o-rings and even tried making a nylon spacer. No luck at all. No matter what I did, I could not keep gasoline out of there.

I did try to find an NOS Rochester B at that time (I watched over several months, actually). I could never find one, although 2 or 3 years later I remember Jon H told me he found one in his shop. Every time I found one listed as NOS the seller could never prove it and there was never a tag on it and it looked more like pixie dust than truth. So, maybe there is one out there but I agree with Jon H. A lot of work to maybe go nowhere.