Wait what?
While the engine is being cranked for start up, the throttles are nearly closed, so atmosphere has a hard time getting by them.Without air going by the low-speed ports, fuel doesn't flow either.
This is where the cranking vacuum kicks in.
Cranking vacuum is created by the ring seal on the pistons and by the closed exhaust valves. If either is faulty, your cranking vacuum is impaired. The rings are sealed by the oil on the cylinder wall. No oil equals no seal. Starting fluid is a fabulous oil solvent, so by now you have no oil on the rings and no cranking vacuum and you can keep chasing your tail around in circles until you get dizzy.
While the engine is running, the oil gets sprayed onto the cylinder walls from spray ports designed and built into the connecting rods. The oil control rings scrape most of it off, and distribute a nice amount to lube and seal the compression rings.
Liquid gasoline does not burn all that well, especially after the most volatile compounds have evaporated off. Fresh gas is CLEAR. It's color tells you how stale it is. It goes from clear to yellow to orange to red. Red is crap. Orange is almost crap. Yellow is trouble in a carb. If you can get it lit inside the engine then you can drive on it, but don't be flooring it.
Leaky exhaust valves can be felt on the end of the tailpipe......IF...... if the exhaust system is sealed, and if the rings are lubed.
Water in the gas is easy to spot; it settles to the bottom and looks like mercury rolling around in the bottom of a glass container, minus the color.
