Yes, that "chemical" is called "water", don't let it get in there. The gas cap has a hole in it. You don't really need to buy stabil if you keep the water out.
Many of these small engines I am fixing were given to me, so I couldn't control what 'fuel' was used in them.
You're "fixing" the carburetors (mostly cleaning) Don't let them sit with water in the bowl, they'll actually freeze into an ice cube in the winter time.
The fact is that ethanol is a problem, especially for older engines (not specifically made for ethanol).
They haven't used rubber parts in decades. The gum is likely varnish from the fuel tank, dissolved by the alcohol. It will be fine once the tank is clean and the filter changed. Run the carb dry when you're done. Put a piece of plastic bag over the fuel tank opening and screw the cap on....take it off before you use it again.
Why do we even have to have ETHANOL ?
Answer #1. You don't, you can buy AVGAS, or boat gas at the marina.
Answer #2. Because the RATs/RINOs, and the ethanol lobby politicized and mandated it.
Answer #3. Because MTBE and lead was very toxic.
Now they've screwed up diesel and diesel engines.
It is not as energy efficient (so to speak) as gasoline. You get worse MILEAGE while using it.
That's because there's too much of it, as a percentage, in the pump gas.
I have been letting you get away with your nonsense, but there is a limit.
Are you aware that the plastic you put over the fuel tank opening will melt and then clog the fuel filter ?
The small engines I have been 'fixing' have had only ONE PROBLEM.
The fuel line OUTSIDE the tank turns hard as a rock. The fuel line INSIDE the tank turns into (freshly boiled) spaghetti noodles. This did not occur before they started putting ETHANOL into the GASOLINE.
I am replacing the plastic (they were never rubber, so I don't know where your are getting that) fuel lines with TYVEX fuel lines. They last longer, but eventually they turn out the same way.
It is not the WATER itself that melts TYVEX nor even the original fuel lines.