Fuel check valve?

[Peter Coomaraswamy]

Just wondering if somewhere in the fuel system there is supposed to be a check valve to prevent fuel from going back into the tank. I have a 74 dual weber set-up and I have a mechanical fuel pump up front and an electric one in the tank that only runs when the starter is cranking. The car starts fine, then after about 3 minutes of running starts to die (usually in a dangerous place) then I crank the starter and it catches and continues to run perfectly after that. I'm thinking that the car starts quickly on the first try so the starter-connected fuel pump is hardly needed, then when the fuel runs out of the carbs I need the electric pump to restore pressure (thus the re-cranking of the starter). I was thinking if there was supposed to be a check valve in the line that would prevent the fuel from flowing back into the tank-any thoughts or do I need to do more gremlin-hunting?

Thanks

 

[Mike Goble]

The short period of time that you are running off the bowls should be very adequate for your pump to suck the lines full. I've used check valves in fuel systems before but only to isolate one pump from the other in a parallel system. There is an overhead in using them as it takes a certain amount of pressure to open them.
I would be looking for a vacuum leak on the suction side of the pump. If you cap the line at the tank and create a vacuum inside the line, it should hold it. If you put your vacuum gauge on the fuel line at the tank then crank the engine, you should have a few inches of vacuum created very quickly.

 

[Peter Coomaraswamy]

Thanks Mike, that will be my first experiment!

 

[Mike Goble]

I clarified my first post to reflect that the line should hold a vacuum, not the tank.

 

[Stevehose]

Your mechanical pump might be leaking internally if the hoses check out.