Return Fuel Line Question, Vapor Lock - Need Help! Options

[Ansbacher]

Now that I am experiencing my first summer here in Florida with my 914 ('74 2.0L Dual Dellorto Carbs), I am running into episodes of vapor lock on hot days (like most days here). I have been reading that even carbureted 914s can benefit from a return fuel line that goes back to the tank, as it keeps the fuel cooler as it recirculates. My question is how to I plumb and route a return line. The old FI return line is present and capped off at the firewall. So, If I add line to that existing line and bring it up into the engine compartment, where do I tap into the existing fuel system? What I have now is: main feed line- a brass "T"- line to the right carb- line to the left carb (with pressure gauge). I am not running a fuel pressure regulator as my pressure never seems to exceed 3PSI anyway. Can a low pressure system use that old FI return that terminates at the BOTTOM of the fuel tank or does it have to enter the tank ABOVE the max fuel level?

Hoping for some answers as it is only getting hotter here by the day. Thanks all.

Ansbacher

[SLITS]

You would need to put a regulator with a return function in the main feed line. The only time it would return fuel to the tank would be when the carburetor bowls are full.

You could change to a higher pressure fuel pump where you regulate the pressure to the carbs at 3.5 psig.

Do you have heat isolators under your manifolds or carbs? Carbs can heat soak if not.

Return line feeds the bottom of the tank.

[jvmarino]

If your pump has been relocated to the front of the car (under the tank), I am not so sure it is vapor lock. I also have a dual Dell setup on my 914, and I had an interesting issue happen one time that led me to do some research on the fuel system. I had a supply line running to the carbs, and no other lines being used (return and vent were plugged).

I had taken a long trip of driving all day, and toward the end of the day, I started losing power and the car wouldn't stay running. I managed to get off highway to a gas station, and started troubleshooting. I was checking fuel pump relays, fuses, looking at carbs, and no issues discovered. Then on a whim, I thought I would check the fuel tank to see if maybe my gauge was inaccurate, and I was empty. Well when I opened the gas tank cap, a loud sucking sound was heard and the tank steel started to make noises as it relieved itself of a large vacuum.

It seems that the gas cap on the car has a pressure relief function, but no vacuum relief function. I guess as the car was running continuously for a period longer than ever before, it had created a large vacuum in the tank, and the fuel would not pump to the carbs. The solution for me was to install a inlet check valve on the vent line, which I had previously capped off (under the engine on the firewall).

This may or may not be happening to you, but it is something you may want to confirm.

Jim

[euro911]

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Do you have heat isolators under your manifolds or carbs? Carbs can heat soak if not. ...

I need to do this … my carbs get REAL hot (IMG:style_emoticons/default/sad.gif)