one way fuel line valve

[Buick35]

On e-bay somebody is selling one way fuel check valves. I'm wondering if anyone tried these and how well they work. If I don't start my old car for after a week or so it takes a long time to start,I think because the gas is running back to the tank. 35 Buick with a Stromberg carburetor.And where should I install them? There's two in the package but probably only one is needed? Thanks,Greg.

[Matt Harwood]

You can buy good low-pressure brass check valves at McMaster-Carr or Summit Racing for $15-20. You might need some additional fittings to make them work depending on how your fuel system is assembled. I used one on my electric fuel pump setup on The Car Which Shall Not Be Named to keep the electric pump from simply pushing the gas back into the tank.

 

 

https://www.mcmaster.com/7775k52

https://www.summitracing.com/oh/parts/crt-169-1002

 

Your problem is not likely to be fuel draining back to the tank, however. Pretty hard for it to go up to the inlet on the fuel bowl, then push all the other gas out of the way on its way uphill back to the tank. What is more likely is that today's fuels evaporate at room temperature. The gas is evaporating out of the fuel bowl, which, after a week or so, leaves it mostly empty. It takes a long time for the mechanical pump at cranking speeds to refill the bowl sufficiently to feed the jets and fire the engine again. Very common problem and I recommend installing an electric fuel pump to solve it. Run the pump for 10 or 20 seconds to refill the carb, then hit the starter and it fires like you just drove it two hours ago. Electric pumps also help with hot fuel situations (incorrectly but commonly called vapor lock) and can serve as a back-up if your mechanical pump fails on the road. I install them on all my cars even if I use them only rarely. Saves a lot of wear and tear on your starter and battery.

[PFitz]

Most likely it not draining back.

Modern volatile gasoline dries out through the fuel bowl vent and jets. A hot shutoff engine will vaporize some of the gasoline in the fuel bowl and push it out through the jets and vent, thus lowering the float level. Using e-free gasoline will help to reduce that tendency.

 

Even if evaporation is not the cause, as the fuel level drops in the fuel bowl the float needle will open and break any syphoning action trying to drain the fuel bowl. Since float and needle are designed to keep fuel bowl levels  close to max, when the fuel level and float drops and the needle opens, that should leave plenty of gasoline in the fuel bowl to start the car and get fuel flowing again.

 

Plus, if the fuel pump is in good condition, the check valves in the pump should prevent back drain. If not, then rebuilding the pump is a better use of the time and money than putting another check valve in the system.

 

Paul

Edited August 22, 2019 by PFitz (see edit history)

[carbking]

Very common with today's gasoline. We get about 5 calls daily on this subject:

 

Gas evaporation

 

The only way gasoline is going to drain back to the tank from that carburetor is if you park the car on its side, and that is kind of hard on the paint job!

 

Take the money you were going to waste on the valve, and surprise your wife by taking her to dinner. The results will be better!

 

Jon.

[JACK M]

Boats with inboard fuel tanks are required to have anti syphon valves at the tank outlet. It looks like any other hose barb.

On occasion the fuel pump wont off set the valve.

 

I have read here about the evaporation thing and it makes sense, But my fleet is about 50-50, half need priming after a week or two and half don't.

However I am seeing a trend towards more priming.

[PFitz]

With all due respect, boats are different for other reasons One main one is any potential gas leaks,  or even fumes, can't fall out the bottom of the engine compartment and dissipate. With boat engine gas tanks and fuel systems, because gasoline fumes are heavier than air and settle into the bilge, where a spark can ignite them, that makes the Coast Guard very fussy about how and what they will allow for fuel system certification.  

 

If the problem was not evaporation and it was the gas draining back to the tank and not leaving enough fuel in the carb to restart the engine and have it run long enough for the fuel pump to start supplying fuel, as Jon pointed out to drain the fuel bowl that much the car would have to be on it's side so that the fuel inlet at the float needle is the lowest point of the fuel bowl.

 

In reality the float needle seat is one of the highest points in the fuel bowl - often being above float level. As soon was the fuel level drops enough to unseat the needle the fuel lines will be sucking air from the fuel bowl's vent system, not fuel. This is basic carbs 101 for both updraft and down draft carbs.

 

The fuel lines can drain back if the  fuel pumps check valves are not sealing as they should. That will not only cause starting delay (only if the fuel bowl level has also dropped due to evaporation), leaky fuel pump check valves can also  drop fuel pressure and lower the float level. That's something the "bandaid" fix of adding an inline check valve,..... won't fix.

 

Paul

Edited August 22, 2019 by PFitz (see edit history)

[carbking]

In the case of updraft carburetors, it was quite common to place the inlet fuel valve in the bottom of the bowl. Since updraft carburetors were lower than the fuel supply system; leakage back to the tank was impossible.

 

Most downdraft carburetors, as Paul mentioned above, have the fuel inlet valve above the fuel level in the bowl, either in the airhorn (top casting) or the side of the bowl, as is the case with the OP's carburetor.

 

The most notable exception is the Rochester Quadrajet, which has a front inlet, and the fuel valve in the bottom of the bowl. When the carburetor was first designed in 1965, a balance type fuel valve was used which did not permit the bowl leaking back. Unfortunately, it didn't seal very well either. When Rochester eliminated the "umbrella" fuel valve in favor of a conventional valve that would seal, the possibility of drain back became real; and Rochester FiXED the issue by designed an inlet fuel filter with an internal check valve. I believe this change was in 1967, but memory is not as good as it once was. This fuel filter with the internal valve is located between the fuel inlet fitting and the inlet fuel valve.

 

The carburetor which was responsible for the coining of the term "leak-down" was the Holley AA-1, used on millions of Ford products, and others, beginning in 1939. But it was not the fuel valve that leaked down; it was the power valve (a.k.a. economiser valve). The power valve in the Holley AA-1 was channeled directly into the throttle area, and if the power valve failed (generally the second backfire, and often the first), the power valve would completely drain the bowl INTO THE INTAKE MANIFOLD. Not a good thing for rings, or crankcase oil.

 

Carburetor bowls MUST be vented in order for fuel to flow into and out of the bowl; otherwise there is a hydraulic lock. The volatility of today's fuel is much greater than gasoline of yesteryear. Couple that with the heat built up in the engine block during running, and one has evaporation through the bowl vent.

 

Different engine styles and different carburetors are susceptible to this evaporation at different rates. For instance Carter AFB carbs, which are some of my personal favorite carbs, are among the worst at evaporation due to the large aluminum fuel bowl. I had to install a full time electric pump on my F-100 with the 390 2x4. This after my curiosity got the better of me one summer day, and I pulled off an airhorn after the engine had been stopped for 30 minutes. The bowl was bone-dry! Not a problem during running and I get terrific fuel economy, just a problem after the engine is turned off.

 

Also "I" engines (I-8, I-6, I-4) have much less trouble with the evaporation issue, as the carburetor generally is not sitting directly above the engine "heat sink".

 

With V-8 engines, Holley 2 and 4 barrel carbs with the end bowls, seem to have fewer issues (at least of the evaporation type) than other 2 and 4 barrels, because of the air gap between the engine block and the carburetor bowl(s).

 

The problem, like others facing our hobby, is not going away; we simply have to recognize the problem, and provide a work-around.

 

Jon.