It started on a hot day after a long drive. I had to stop for a red light and by the time the light turned green the car ( a '74) stalled because of vapor lock. There was a drug store right across the intersection so I went and bought a gallon of water to dump on the fuel pump to cool it down. It started and stalled a few times but eventually I got it running and made it home.

I decided I had enough of vapor lock problems and bought an electric fuel pump with the intention of running it in-line with the mechanical pump just to get some liquid gasoline to the mechanical pump so it could do it's job. To install the electric pump I had to drain the gas tank so I decided to drive the car on a parts run to use some of the gas before siphoning the rest off. Well, I didn't make it too far and it vapor locked again. This time I had taken a gallon of water with me so I dumped it on the fuel pump and made it home again. When I was dumping the water this time, I noticed that the "S" lines to the mechanical pump were cracking so I changed my plan and decided to just go with the electric pump with a bypass pressure regulator and a return line. I mounted a 100 micron filter before the pump with the filter lower than the outlet from the gas tank and the pump lower than the filter so the gas from the tank would feed the pump because of gravity. I did this because electric pumps "push" the gas whereas mechanical pumps "suck" the gas from the tank.

So now it was time to fire it up. I put 5 gallons of gas in the tank and tried to start the car. The pressure gauge at the carb was showing zero pressure even though I could hear the pump running so I started troubleshooting. I found that there was no gas coming from the tank even when I took the hose off the outlet from the tank. I tried to clear the line with a shot of air from my compressor and sure enough gas started to flow freely. I put the lines back together and was able to start the engine.and I ran it in the driveway for about 15 minutes and all was well. I shut it off, closed the hood and let it sit for about 15 minutes to see if it would vapor lock and it started immediately. I thought the problem was solved to I headed out to the gas station to fill up and I got about 2 miles farther than the last time and it stalled on me again only this time I didn't have a mechanical pump to cool down with water so I had to have it towed. I was thinking that the filter screen attached to the pickup on the fuel sending unit must be clogged, but I was able to blow air through it (which probably pressurized the tank and pushed some gas into the fuel line). It would not have stayed pressurized for long because I have a vented gas cap.

The other thing I noticed is that the fuel pickup line inside the gas tank goes up maybe 4 or 5 inches and then comes back down to the filter sock. That being the case, there won't be any gravity feed unless you have enough gas in the tank to cover the highest point in the fuel pickup line. That probably explains why there was no gas coming out of the tank when I removed the fuel line but does that mean the car will lose pressure any time the fuel drops below that level? It looks like it would take almost half a tank to be above the highest point in the fuel pickup tube.

Has anybody installed an external electric fuel pump? Does anybody know if the fuel will siphon through to the fuel pump once it gets started? It seems like that should have happened this morning but apparently it didn't. Does anybody have any suggestions for what I should do next?

I have been a member for a long time but haven't been active for several years. I hate to admit it but this time I'm stumped.

Thanks and any help will be appreciated.

 

I had a vapor lock problem on my 68 convert with bb, especially if the car sat for 15 minutes when it was hot. I installed an electric fuel pump and it has corrected the problem. It sounds like you may have a problem with the fuel lines being partially clogged with dirt or debris. I would flush them with compressed air, replace all of the flexible rubber parts and then make sure you are getting gravity flow without the fuel pump running. Install the electric pump at the lowest point you can find a place to fasten it to the frame or a bracket you make to fasten to the frame. I installed a pressure regulator and fuel pressure gauge just before the supply line goes to the carb so it is possible to check if enough fuel is going to the carb. Hope you get your problem fixed.

 

I have already done most of that. I didn't try compressed air in the lines but I don't seem to have a problem getting fuel to the front of the car once I can get it to the fuel pump. That certainly will be something I test when I work on the car again (probably Monday). Everything from the tank to the fuel pump is new except for the sending unit/fuel pickup in the tank.

Let me ask a couple questions:

Do you think my filter sock could let air through it backwards but not let gas through?

Do you experience any fuel issues if your tank gets low?