2 Cycle Phase Separation
The engine to the right has been destroyed from phase separated fuel. Ethanol is hygroscopic (absorbs water), the vial to the right is from the fuel tank of this engine. The fuel on top is gold in color because 2 cycle oil will only bond with the gasoline. The octane is also lower because the ethanol has separated from it and bonded with the water below. Approximately ¾ of the clear fluid in the bottom of the vial is ethanol. The ethanol water mix settles in the bottom of the fuel tank and is picked up by the fuel system, then delivered to the carburetor. The engine ran on this ethanol mixture, causing it to run extremely hot with no lubrication. This damage occurs in only a few minutes of operation. The engine also ran out of control, which poses serious safety concerns for the equipment operator.
4 Cycle Phase Separation
This carburetor suffered from severe phase separation. More than likely, rain water entered into this fuel system, creating the severe corrosion you see. This carburetor cannot be repaired and must be replaced.
Engine Failure from Varnished Fuel
This piston and crankshaft assembly came from a 2-cycle engine that ran on stale fuel. The engine was hard to start and had low power. It ran long enough to gum all of the internal components, including sticking the rings.
Why bad gas occurs
The problem with gasoline containing ethanol (E-10) is when it is left standing in a fuel system for long periods of time with fluctuations in temperature & humidity -- the fuel will start to decay in as little as 60 days. What would happen if you left milk in the back of the refrigerator for 60 days? E-10 gasoline decomposes the same way, just not as visual -- a foul, sour smell is prevalent when E-10 is decaying.