Negative on your conclusion about the heigth of the pump relative to the fuel level.
Here's what can and will/does happen.
If the column of liquid fuel is exposed to a "mild" heated ambient atmosphere you are correct, small bubbles can/will be formed and you're also correct they will be evacuated thru the carb vents to atmosphere as they're pushed along by the moving fuel.
However, here's where your explanation goes astray: When the fuel boils at a lower temp (like today's fuels do) and the fuel delivery system is blistering hot (like the underhood with our newer higher temp thermostast and sometimes overheated engines due to coolant contamination)then you have a situation where every drop of liquid is being converted to gas (vapor) and there's nothing left to push with!! Eg. there is no liquid in the line, all the fuel in the line is converted to vapor and the pump cannot continue to pump when there's nothing in it but vapor.
Thus as long as there is some liquid remaining in the line you are right. If conditions are such that every drop has been converted then you will have very serious and terminal vapor lock.
Regards
Ken Michael
PS the secret to success is a return line to the tank which will keep fresh cooled fuel always moving in the delivery system. Tap it off just before the carb inlet and you form a lop of cool fuel. DO NOT SHORTCUT THE RETURN TAKE IT COMPLETELY TO AND DUMP IT BACK INTO THE TANK.
Posted on Aug 5, 2009, 1:24 AM from IP address 207.192.248.14