Let's not needlessly over-complicate the subject about low cost carb cleaning with your concerns about types versus families, it's just non-practical as the "type" I'm referring to is either common Buna-N or Viton o-rings.
Based on when these carbs were designed and built I feel my statement wasn't inaccurate, as for simplistic, in the context of what is being discussed it would be appropriate to what this post is really about which is not a full blown analysis of elastomer technology.
I merely responded with what I know when the dreaded which material is best scenario popped up. (just like oil and tires) By the way where did you get the sales numbers that 3M is out selling Dupont in fluoroelastomer's, I'd be interested in seeing that as Viton is heavily ingrained in industry by name recognition?
I have to ask, is anyone here really going to go out there and demand to know how much acrylonitrile is in the composition, what other additive compounds or single polymers are in the o-ring compound they have in there hand? Nope, just "is it good ol' commercial Buna-N and Viton" is what you're going to find. Durometer is far more important than composition of the material as long as it is readily referred to as Buna (nitrile) or Viton.
Fluorocarbon compounds have a higher than normal mold shrinkage rate, as a result molds for fluorocarbon products are often made different from molds for Nitrile based compound seals to try and compensate for this with some degree of success. Take the same size Buna-N and a Viton o-ring, mic the cross section, you'll find the Viton is on the low side of the nominal tolerance each time compared to Buna-N (it gets much worse in cup type seals).
Why I would recommend generic Buna-N o-rings over Viton in your carb rebuild? You can find them on a Sunday afternoon for one, it doesn't get hard and leak at -15°F (good for our Canuck friends to know) and since these old carbs were engineered with Buna-N nominal tolerances in mind you won't have to deal with any stretch or failure to properly compress potential when installing them.
For those considering using white vinegar or lemon juice, it won't hurt the metal as the acid concentration is too low (about 5% or less) as well as the duration of exposure. If you're paranoid you can use baking soda to neutralize any residue in one of your rinses, in fact there is a process that a now deceased fellow in Norway used to use that was just baking soda and boiling water that made his carbs look like new. I'll find the link if anyone is interested.
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