I recently had a problem with my JEEP where it would be running perfect, then all of sudden act like it was starving for fuel, then quit. When trying to restart it, it would sometimes fire up and idle but had no power and then quit running again. If I pulled the choke it might run and quit again. Removing the air intake horn would show I was getting no gas into the carb. But then, after trying and trying and cranking and cranking, it would fire and run and off I went. Sounds like vapor lock, right? Or something clogging the fuel line, possibly. After this happened the third time and I needed to be towed home (very embarrassing with less than 650 miles on my rebuild), I had to figure out what was wrong. I drained the tank, blew out the lines, changed the fuel filter. I didn't really think I needed to replace the fuel pump being as new as it was but decided that I don't want to get stuck on the road in a bad situation. I had been very lucky the first three times. Besides, mechanical fuel pumps don't quit and then start working again. Electric, sure, but not mechanical. So I bought a new one anyway. When I picked up the old pump to remove the brass fittings I noticed a rattle. I picked up the new one and noticed it did not rattle. Ah-ha! This could be my problem. So I decided to investigate. I pulled off the top cover and found this. Having never taken a fuel pump apart before I did not know what I was looking at but could see that it was loose. So I took the next two pieces apart. I don't think this is supposed to be floating in here. It appears to me that, strange as it may seem, the valve was popping out of its hole and causing the fuel loss. But then, while trying to restart it the diaphragm was pounding hard enough on the valve that when it would float or move into the right place it would pop back into the hole and stick well enough to allow the fuel to pump again and let the engine start and run. Just the slightest pressure would hold it in its hole for awhile and with the diaphragm so close the valve could not get far from where it should be. I was actually able to reproduce that it my hands. You can kind of see in the picture above that the valve is not very deep in the recess, but it was stuck well enough to need forced out. So if you have one of these superior quality pumps, keep this in mind next time you think you're getting vapor lock.