A couple of people sent me questions regarding my earlier comments on =
vapor lock, so I thought it would help to clarify a couple of points...
Fuel pumps still tend to pump whatever is in the fuel line, even if it's =
mostly vapor. However, their efficiency tends to go down when pumping =
vapor instead of liquid fuel. Fuel vapor is much less viscous than =
liquid fuel, so, for example, if the check valves in a diaphragm-type =
pump don't seat perfectly due to wear or debris, the pump will be much =
less efficient trying to pump vapor through it rather than liquid fuel. =
The vapor simply leaks more quickly through any open areas at the check =
valves. On the positive-pressure side of the pump (between the fuel pump =
and the carb), some of the vapor may condense back into liquid fuel, due =
to the higher pressure. However, if the check valves are worn or dirty, =
it won't be able to build up as much pressure on the positive side and =
it is more likely that less of the fuel vapor will condense back to a =
liquid. Of course, if the fuel line between the pump and the carburetor =
is hot enough, even the extra pressure won't condense the vapor and =
you'll still end up pumping vapor into the fuel bowl instead of liquid. =
And if the carb is hot enough, liquid fuel can turn to vapor (boil) as =
soon as it enters the carburetor.
Naturally, if the fuel lines or carb are hot enough, even the best fuel =
pump won't help. You've gotta have liquid fuel in the carb...
Many newer vehicles have fuel pumps located inside of (or next to) the =
fuel tank. One reason for this is to produce positive pressure =
throughout the entire fuel line system to help eliminate vapor lock.
One other thing...
If you have a restricted fuel line or clogged fuel tank vent cap, a big =
enough vacuum can build up in the fuel line between the tank and the =
fuel pump, even in moderate temperatures, to cause vapor to form. And it =
is possible that the vacuum may become high enough that the fuel pump =
simply can't overcome it and pump enough fuel to the carburetor. A =
===
To unsubscribe from the mil-veh mailing list, send the single word
UNSUBSCRIBE in the body of a message to <mil-veh-request@skylee.com>.