[rotorwrench]

Small engines have very small passages in the little plastic carburetors so if they get varnish or crud build up, eventually they will no longer pass gasoline properly. This makes it a very good idea to store small engines with no fuel in them.

Modern fuel is a lot different than it was 30 or 40 years ago. It has a tendency to deteriorate with any outside air contact. It will turn to a mixture that smells like turpentine within 6-months. The best fuels available at the pump are those that are marketed as 93 octane since it is a more stable fuel but also more expensive. Fuel with ethanol deteriorates faster than fuel with no ethanol. The ethanol absorbs the condense and becomes more dense so it rolls around in the bottom of the tank and picks up old crud plus it can suffer from some microbial growth making the mixture like fuzzy blobs that roll around in the tank with motion or movement from normal driving conditions. The stuff also tends to get acidic and can create more problems with the fuel system over time.

Avoid ethanol fuel or use premium fuel. That's about all you can do to slow fuel deterioration to a minimum.

Model A fuel tanks will still have an area on top inside that will condense water out under the right conditions even when full. It's very hard to stop condensation unless you control the climate in your garage.