It is my condsidered opinion that Vapor Lock can not exist in and automotive fuel system in which the fuel pump is at aproximately the same level as the fuel tank.
We all know the Ford flathead 8's had fuel problems related to heat, but their fuel pumps were mounted high on the engine and higher than the fuel in even a full gas tank. And due to the limits of the specified carburetors were only developing 1.5 to 2 lbs of pressure. Another example of Ford's less that stellar engineering. But I digress.
fact: A bubble of air, or other gas can not block a fluid under pressure where the fluid under pressure is exiting to the atmosphere.
fact: Carburetors vent to the atmosphere.
Proof: Bleeding brake lines, visual reference open a beer or other carbonated beverage and watch the gas bubbles go to the atmoshpere.
Fact: fuel pumps are made to pump fluids not air, our pumps operate at 3 to 7
lbs per sq in of pressure which will easily push a bubble through a column of fluid.
Supposition: The condition most non ford people attribute to "Vapor Lock" is likely air entrapment in the fuel pump. The source of the air is likely a leak in the fuel line between the tank and the pump. Which asks the pump to pump air rather than the fluid it was designed to move. Or the residual gas in the pump is vaporizing (much more common with today's fuel formulas) and building a bubble on the inlet side of the diaphragm. Where the gas is not under pressure.
Fix: Find and repair any air leaks in the line. and/or Install a heat shield between the exhaust manifold and the pump.
Another hot start problem asociated with today,s fuel is perculation. The fuel in the float bowl absorbs the heat from the engine compartment, expands spills over into the manifold. Then the float drops, residual pressure from the pump refills the float bowl, and the cycle repeats, flodding the engine. Check for raw fuel around the throttle plate pivot to attest to this problem. If so when hot starting, treat the engine as flooded and do not pump the gas gas pedal, instead, hold it WOT befor and while cranking the starter. To mitigate the problem, reset the float level to one which is slightly lower than factory spec. which will shut off the needle and seat before the bowl overfills. And you can fashion a heat shield that goes between the manifold and the float bowl.
Soap Box under the bench. Thank you for your indulgence and good evening.
Posted on Jul 5, 2009, 8:35 PM from IP address 67.249.224.100