earlwb

Timbli,
That might be the problem. I suspect that since the vast majority of the carbs are made in China, that it really depends on the engine manufacturer's specs as to what the materials are they used for the rubber parts inside. I can see the utility engines like weed wackers and chain saws using better parts. Plus the high end RC gas engines, I assume, would use the better parts. But the low end engines would be very questionable as to what they used inside the carbs. The Viton seals and gaskets do cost more so I can see that being a cost cutting measure. That is one reason why Walbro has a seemingly endless variety of carbs for engines where it depends on what the vendor or manufacturer wants.
The Chinese still use a different gasoline than we do, but the SEF gasoline I mentioned above smells a lot like the gasoline the Chinese use, as I have a couple of engines that came from China that had been test run at the factory using Chinese gasoline. So in China they may not have any problems with the engines and carbs like we could have here. Normally a person would not think anything of it with the gasolines being different from each other around the world.