Fuel Return Line

[ch33kster]

Hello one and all!

I have recently upgraded my carb to a 32 ADFA 14 on my 69' 124.

The problem that I'm having is the fuel return pipe has no where to go to as the tank doesn't have a return inlet. Although I'm considering running a return line back along the car and into the filler neck I was wondering if there was an easier way around this by attaching a 'Y' joint before the mechanical pump with the main fuel inlet pipe connected to one side of the V and connecting the fuel return to the other side (see the picture).



The return spurts out fuel. I'm unsure wether it would flow ok, if there will be enough suction and if it would be safe.

Cheers guys, always appreciated.

PS I know the carb illustration looks like a gun wielding Zorro.

--------------UPDATE------------------------------

I have just seen KalamazooJohnny carb pipe layout (Pictured below) on his 32 ADFA. Should I panic, the only pipes I have to connect to are the fuel in and fuel return and the two coolant ports on the choke.

[TulsaSpider]

When I got my car, 78. it would start but not keep running. All the fuel would simply get diverted back to the return line. So I simply plugged the out nipple. Problem was solved.

[manoa matt]

What type of fuel pump are your running, electric or mechanical? Electric pumps don't "necessarily" require a return line, but mechanical pumps do.

[TulsaSpider]

Mine was mechanical-?

[manoa matt]

Tulsa, Either your needle valve was old or stuck, or your return line did not have a check valve.

[ch33kster]

Thanks for your replies. The pump is mechanical.

One other element I thought of adding was a check (non- return) valve in the return line before the 'Y' junction.
manoa matt, is this what you meant by the check valve location?

Logically, would this work, in theory it should but would the pressure/flow be too much for the mechanical pump?

[manoa matt]

On the stock setup the supply and return lines were completely separate, however you diagram seams plausible provided there is a check/non return valve in the return line before the "Y" junction. Without the check valve you would simply be splitting the supply line and feeding the carb from both lines.

Hard to say if there will be too much pressure for the mechanical pump to handle, probably not. Typically the fuel filter goes between the pump and the carb, mechanical pumps work on suction, hence why they are at the end of the line near the carb. While electric pumps push and are installed near the tank.

[majicwrench]

With the Y before the fuel pump intake I see no need for a check valve. There is no pressure in that line, so it would never feed the carb from that. Feeding back to the fuel pump inlet/intake port is basicly just like feeding back to the tank.
Most cars had fuel returns to help combat vapor lock. By constantly running cool fuel thru the pump and line it kept everything from boiling. You may be more prone to vapor lock just feeding back to the intake of the pump, but realisticly it should work fine.
Keith

[ch33kster]

Cheers guys! Im going to give it ago and see how she runs. I was starting to think of running a line straight back to the tank as it should be but not on 69' AS models. This technique is to save time and is a short cut I suppose. The vapour lock does concern me, I had issues with fuel starvation / vacume leakage last year which is partly the reason for the carb update. I will keep you posted. Thanks once again.

[ch33kster]

Ok, I set the fuel lines up using the 'Y' connection as shown in my diagram and it wouldn't pull fuel from the tank at all. Not sure if this was the vacum lock. I have returned a fuel line all the way back to the tank and it seems to be running ok.

One other thing to note is that I thought that all the valve ports were blocked off apart from the Fuel in and fuel retrurn. There was another that was hidden away near the base under the fuel valve ports. This needs blocking off.

[majicwrench]

I see said the blind man...
OK, now I see why you need a check valve--duh.
Glad you got er goin!

[manoa matt]

There are two ports "hidden away" on the front of the carb near the base. The one near the drivers's side fender should be hooked up to the air cleaner if you have a stock air cleaner it's the small port. It helps to draw engine vapors from the crankcase, hence why its "t'd" into the crankcase port. If you have a non stock air cleaner, you can block it off unless the air cleaner came with a fitting where it locates a small port next to the crankcase breather tube.

The other port is near the base on the passenger side of the carb is for the fast idle system. A hose should go from that port to the electrovalve located on the drivers side fender, it should be the rear one. A hose exits the back of the electrovalve and is connected to a port on the intake manifold.