[Tom Vaught]

I will make a few comments tonight on fuel and its ability to be ignited by a spark or by a flame.

Before Gasoline (or other fuels) can burn Vaporization of the fuel is required.
Vaporization converts the fuel into a gas state and this only happens when the liquid absorbs enough heat to boil.

Temperature and Pressure relationship comes into the discussion.
Water for example will boil at 212 degrees F and at sea level conditions.

Take the same water and try to boil it at Denver and it will boil at a lower heat temperature.

In cold weather the fuel has a harder time of vaporizing and the fuel burning which is why you have heated intake manifolds.

Obviously you would think the higher the temperature the better the fuel vaporization, (but the reality is if all of the fuel is vaporized there will be a loss in power of the engine.
The Charge Density goes down. You have a smoother running engine but with less power.

On a engine with a carburetor, the intake manifold walls will always have some fuel clinging to the surfaces. When you accelerate the fuel gets removed from the walls for an instant. That fuel needs to be replaced or you get a lean condition in the engine.
The accelerator pump circuit replaces the fuel on the walls with new fuel and adds a bit of extra fuel to the intake charge for a slight period of time. Not enough fuel replaced and you get a engine hesitation.

One final comment for tonight:
Imperfect Vaporization may occur if:

a) The Mixture Velocity is too low
b) The Intake Charge is too cold
c) The Manifold Vacuum is too low
d) The Fuel Volatility is too low for the ambient temperature.

Have a good night.

Tom V.