You are right. Always do the simplest thing first. Of course I checked the valves - even removed them and looked under the hand lens to see that they were seating...but it's still the most likely culprit. Especially since this is such a slow leak.
Searching internet, it seems that leaking down is a weirdly common problem with small tires. Especially with things like garden carts and wheelbarrows that use these similar "made in China" small tires. It's typically a very slow leak and may take a month or more to go flat. But the result is the same. The valve stem is as good a suspect as any. These valves look good, have nice dust caps, and all pass the spit test....but good looks don't keep them from going flat. I'll replace the valves on general principles.
Being a curious type guy, I wonder why these Chinese tube type tires all leak? Since it's such a common malady my guess is that it's some mistake in the manufacturing process. I'm old enough to remember when Japanese equipment was almost all junk; things would fail because the maker had overlooked some simple but essential step that a more technological society- like the USA of the time - had solved many years before. Imported parts looked the same but didn't work the same.
That's not the case today, of course. With that in mind, I'll replace those valve stems even though they look perfect. In fact, I'll probably have to replace the Chinese ones with "made in Japan" parts!
At least I'll know the replacement valves will be made right..... Now how's that for irony?
And I'll still look around for some sort of injectable tube sealer or maybe even some sort of "foam in a can". There's no real reason why they need to be 100% pneumatic type. Maybe the offroad motorcycle or bicycle shops have the right goo.
Tires are 4.10/3.50 X 4" & rated at 30 psi. I usually run them at 10 psi or so.
rScotty
