Quote:
Originally Posted by Mountain Dew
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Why did the vapor stop at the filter? Why didn't the vapor pass through the fuel line and vent through the gas tank?
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Quote:
Originally Posted by BILL WILLIAMSON
The pressure of the column of gas above the filter had it blocked, like you can't burp while rapidly chugging water! Bill W.
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I think Bill answered it. My only quibble would be with the word "rapidly"; if there were
rapid fuel flow holding the bubble down, there would be no problem. In reality, the fuel flow around a bubble might or might not be enough flow to allow the car to sputter along.
Quote:
Originally Posted by BRENT in 10-uh-C
Steve & Gary, ...using your scenario of vaporization in the fuel line, please explain exactly what is happening in your view? I understand the air pocket in-between two liquids, but what is happening when the lower level of fuel in the fuel line depletes? A Model-A carburetor will still perform with a bowl half-full, and as soon as the float drops pulling the needle down, you really shouldn't have any more backpressure to hold the "air bubble" (vapor) in the line. (Remember the bowl is vented where it cannot hold pressure.) So again, would somone please explain in minute details exactly what is happening from the beginning until the end as to why this is called 'vapor lock'?
As far as not believing that percolated fuel can be sticky, all I can say is try it like I did several years ago. Pour a little gas in a bowl off of a Zenith carburetor and warm the bowl. I used a very small flame but you do whatever you feel comfortable with. Just waving the heat under the bowl will cause the carburetor bowl to become extremely warm all over. I just got it hot enough that the fuel simmered and evaporated. It doesn't take long for the fuel to disappear ,and as it was cooling down I stuck my finger in the bowl and the floor of the bowl was sticky. Again, for those that don't subscribe to my theory, then so be it.
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Maybe a less graphic example than Bill's would help folks accept the fact gravity doesn't always win. Surely, we've all experienced a sink being blocked by an air bubble "trapped" under an "open" stopper; it won't drain until the stopper is jiggled around to let the air burp out. That is a gravity flow system, with liquid above a bubble, and an open vent below the bubble--sound familiar? It happens, guys.
If you want a more scientific explanation, I think it has to do with surface tension of bubbles. Before a big bubble, like that under a drain plug in an inline filter, can either squeeze by the plug or up a skinny fuel line, it has to undergo an energetically unfavorable decrease in radius of curvature. I'm not saying I totally buy it, but if someone needs a theory before they can believe their eyes, there you go.
Regarding your percolation theory, I don't doubt that a bit of sticky stuff will be left when gasoline evaporates. The part I don't understand is how that sticky stuff gets up on the shut-off valve when the evaporating puddle must be primarily down in the bottom of the bowl.
Semantics: This isn't important but I don't underdstand use of the term "percolation" to describe boiling off the fuel in a carb bowl; as I understand it, it's not much like what goes on either in a percolator coffee pot or in a septic bed perc test. I realize that our use the term "vapor lock" to refer to any issues deriving from unwanted fuel vaporization (including percolation) also can be criticized.
Earlier you asked how riding the choke could possibly help a vapor lock situation. My guess is that it simply takes what meager fuel is available and adjusts the air/fuel mix ratio to something more useable. Clearly, as you say, if there were complete "lock" of fuel flow, it wouldn't help, at least not for very long.
So many threads--so little time.
Steve