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I was not saying that vapor lock does or does not exist, I was simply asking for someone to logically explain how it can happen in a gravity feed system. What I'm having trouble understanding is how the carb could become dry. The needle valve can not shut off air if the bowl is empty, full of air, or even a bit low due to the "crap" fuel boiling, so assuming it's open, it would'nt be long until fuel from the tank or line filled the bowl with fuel, or even a mixture of air and fuel. This flow can only be stopped by the needle valve when the bowl is full of fuel. I have driven flatheads for many many years and have been let down five times. All five were ignition problems (hot coils) and none were "vapor lock". Back in the day you would always hear about vapor lock and how it was fixed by putting a dime in the fuel pump arm, or wrapping the lines with cold rags etc.,but whatever the remedy, it usually took 15 to 20 min., which is just about the length or time required to let the coil cool down. Messing with the fuel pump could have been replaced by changing a tire or going for a stroll down the road and back, all would have had the same effect. A friend of mine with a Hershey winning '34 Phaeton just experienced "vapor lock" and almost killed the battery trying to restart it after a short stop. Fortunately it came to life after a very short push. What really happened was that the hot coil would not fire as the hot motor drew too much out of the battery. He now carries a spare coil and no cold rags or fuel pump saving dimes. Still waiting for that logical explanation. Cheers : Bruce