The primary source of the vapor bubbles is the Butane in the gasoline.
This is the "Starter Fluid" component of gasoline.
It has a Boiling point at ambient Pressure of just a hair under 0°C.
It acts similarly to dissolved Carbon dioxide in a soft drink.
You will get a lot of "Fizz" as it exits the Pressure regulator or the Bypass orifice.
You would get the fizz in the fuel pump but the increase in pressure keeps it in solution.
Gasoline in the northern climates get an increased dose of it in the fuel during the winter month partly because it helps with cold starting but mostly because it does no harm as long as the fuel remains below ~25°C (~80°F) and mostly because it is cheaper than the other components in gasoline.
Notice that Gasoline is less expensive during the winter months in areas where tropical temperatures are unlikely.
While it readily vaporizes above freezing at ambient pressures, it vaporizes vigorously at even lower pressures.
The MAP pressure in an idling engine routinely approaches 10"hg.
At his pressure Butane "Boils at ~ -20°C (~0°F) making winter starting easier.
This also explains why a frozen engine will idle but will not rev-up; opening the throttle raises the pressure and halts the evaporation.
Once the intake manifold warms-up the engine runs as if it were summertime.
The next time you find yourself warming up the car, consider what you are really want to warm up is the intake manifold as the car does not really care how comfortable you are.
