'72 250 Zeniths - Fuel return valve question

[rgnprof]

My Zeniths (1972) have the triangle shaped, rubber diaphragm fuel return valve. Can anyone explain how this thing works? I consistently have problems with this thing leaking - both from around the edges and from the connector hose that leads back to the front carb. I suspect that I have some slight warpage, or even some surface imperfections, scratches. I have tried some light sanding with 320 grit paper - will see if that helps.

I have a new rubber diaphragm in place but the thing still leaks around the edge. I'm thinking of fitting in a paper gasket cut to fit around the outside and then I will install the rubber one over it. Not sure if this will work - it's either this or try some gasket sealer, which I'm really not sure about.

Any advice?

ryan

[t walgamuth]

I have never thought about the details of one of those valves. I suspect it has some kind of reed valve with a spring holding it which will hold the pressure needed to make the carb work correctly while allowing pressure higher than that to permit the excess fuel to move on and back to the tank.

The only thing that matters in your case is that it is under some pressure whenever the car is running excepting perhaps under full hard acceleration when the carbs might actually use all the fuel available (actually probably not too likely, IMHO).

If you are sanding a flat mating surface be sure to use a block.

Good luck.

[mercmad6.3]

Theses are essential for the smooth running of your car. Check that the diaphragm is fitting tightly all around the valve body .If the hoses are leaking ,buy new ones.Being directly over the exhaust manifold should convince you that leaking fuel is a bad deal
To prevent fuel from leaking from the valve ,smear some hand soap that you have softened in water ,around the sealing edges,it will prevent the fuel from leaking.
Make sure that when the engine is idling the valve is open and letting the excess fuel flow back to the tank.

When the accelerator is opened the valve should close giving full fuel pressure to the carbs. Fuel pressure is only 2-3 PSI so any leak through the valve will make the car sluggish.

[rgnprof]

Well, I got it to stop leaking. Pulled the top two sections of the carb several times to get it done though...

Sanded the surface smooth and cut a paper gasket from some fuel resistant gasket paper. Put the rubber diaphragm over it and it's not leaking - finally! I have no idea if the thing is working properly - but I'm still not sure what it does! Car runs fine...well, pretty much like it always has.

ryan

[cth350]

That little brass valve has a simple diaphram that when pressed in by a lever on the carb's linages lets fuel flow back to the tank (at idle). With the throttle activated, the valve goes back to its rest state and fuel flow is blocked.

I haven't looked at one lately, but the banjo fitting between the valve and the carb should be sealed with a pair of aluminum seals. Be sure to tighten carefully, since both the brass and the carb body are light enough to be destroyed by a heavy hand.

-CTH

[rgnprof]

No banjo fitting on mine - mine is the '72 32/40 INAT's with the triangle shaped rubber diaphragm on the front carb.

[todds]

Yeah, the brass valve that contacts the linkage at idle is the older type fuel return. I think the newer style is a simple metered orifice, dunno exactly because my carbs all have the older one.