fuel pump leaking

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adamhut
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Joined: Sat Jun 21, 2014 11:42 am

fuel pump leaking

Post by adamhut »

1963 Sypder

Today I started up the car as usual, about once a week in these winter months. Started on first try, as always, and everything seemed fine. I let it sit for a few minutes and started doing something else, and then I noticed a puddle of liquid under the car (turned out to be gas). Opened the lid and fuel was streaming out of the mechanical fuel pump. Car was idling fine for 5-10 minutes just fine. Turned car off and investigated a little. It seems the fuel pump is working fine except fuel is leaking! Any advice?
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bbodie52
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Re: fuel pump leaking

Post by bbodie52 »

Where is the fuel leaking from? The cross-section illustration below should give you some idea of the internal structure of the fuel pump. If the fuel is leaking form the vent hole in the top cover, the upper internal diaphragm may have torn or ruptured with age. Fuel pump rebuild kits are no longer manufactured.

The stock Corvair mechanical fuel pump has proven itself in performance and reliability for decades through millions of Corvairs. There is a tendency to quickly abandon it and go running to an electric fuel pump replacement at the first sign of apparent trouble. Old age can certainly be a drawback or weakness with this pump, but many continue to survive and perform well. There was certainly a history of poor quality aftermarket replacement pumps that developed a bad reputation for a while, and unfortunately rebuild kits are no longer available. But if you begin having what appears to be carburetor problems, don't be too quick to condemn the pump.

There are two relatively simple tests outlined in the Corvair shop manual. These tests measure output pressure and fuel delivery volume. The output pressure test utilizes a common vacuum/pressure gauge that is relatively inexpensive. The output pressure is regulated by an internal spring that is contained in the upper pump housing. Unless your pump springs a leak in one of the diaphragms or seals, it is likely that the output pressure will not change with age. However, new pumps may be fitted with a spring that produces an output pressure well in excess of the 4-5 psi standard. High-pressure can cause carburetor flooding, and is particularly a problem with the Carter YH carburetor found on turbocharged Corvairs, which is sensitive to excessive fuel pressure.

A new fuel pump should always be tested for output pressure. If the pressure is found to be excessive it may be possible to cut the spring or to exchange the spring from the old pump and fit it into the new pump. This may correct the output pressure.

The second test measures fuel flow at the fuel pump outlet. The standard in the shop manual states that the pump should be able to deliver 1 pint of fuel over a period of 40 seconds or less at engine cranking speed. If your pump does not appear to have any leaks and can pass the output pressure test, but fails to deliver the needed fuel volume, the problem may not be with the pump itself. There is a long fuel line that runs the length of the car from the fuel tank to the fuel pump. In order to pressurize and deliver fuel to the carburetors, the pump must be able to create a continuous vacuum in that fuel line to draw the fuel from the tank to the pump. Most of the fuel line is made up of steel tubing and is unlikely to develop a leak. However, there are two short lengths of rubber fuel hose in the fuel path. One section of hose is found at the fuel tank outlet, while the other is found adjacent to the starter motor — just before the line enters the engine compartment. The purpose of the second hose is to absorb vibration from the engine and prevent it from reaching the rigid steel fuel line. If either one of these two hoses develops a leak, the leak itself may not be apparent because the line is not under pressure so fuel will not be forced out. Instead, the leak amounts to a vacuum leak, which can allow air to enter the fuel line. This can prevent fuel from being drawn from the tank to the fuel pump, much like you might experience with a drinking straw if the straw was to split and developed an air leak in the side of the straw. What appears to be a faulty pump that is causing fuel starvation problems in the carburetors often turns out to be a leak in the fuel line at some point between the gas tank and the fuel pump. So if fuel starvation becomes a problem with your carburetors, there is a tendency to question the condition of the needle and seat valve inside the carburetor, or to blame the fuel filter at the carburetor inlet (thinking it is clogged), or to blame the fuel pump itself. Before you blame the pump and toss it, or abandon it and replace it with electric fuel pump, be sure to check the condition of the rubber fuel hoses at each end of the long fuel line between the fuel tank and the fuel pump. You may find that a couple of hose clamps and a few inches of replacement fuel hose is all that necessary to get you back on the road!

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Also, if you have any reason to remove and reinstall the fuel pump, be sure that you have installed it properly. I would confirm that the fuel pump is correctly seated and installed. There is a hole in the side of the pump shaft that the tapered bolt tip must seat into. If the pump is sitting too high and the bolt is simply pressing against the side of the pump housing, rather than seating inside the tapered hole, the pump push rod will not be doing its job. So first confirm proper pump installation, and then check the fuel pump output pressure and volume, as shown in the shop manual pages above. Fig. 57 in the shop manual page shows the tapered hole that the tip of the bolt fits into. This ensures proper installation and seating of the pump.

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If you replace the fuel pump, be sure to check the output pressure of the new pump. The spring determines the output fuel pressure, and new production pumps sometimes produce to much fuel pressure. The Carter YH carburetor is particularly sensitive to excessive fuel pressure. If you find that the pressure exceeds the standards outlined in the shop manual, you might be able to solve the problem by swapping the spring from the old pump.

:link: http://www.corvair.com/user-cgi/catalog ... IN&page=65
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Brad Bodie
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66corsaguy
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Re: fuel pump leaking

Post by 66corsaguy »

I’ve had mine leak before also. They are the strangest things. There’s a story that there was a bad batch made a long time ago and you may have one or it’s just old. I’ve been told to let it sit and next day magically it fixes itself. If it does not fix itself you can tamp the bolts down a little more. If that does not fix than its time for a new one.
I would only order from Clark’s. Because of the bad batch your local auto parts store may still have from the bad batch personally for this part i bought from Clark’s and it’s been good. I bought from LAPS and it failed also.


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adamhut
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Re: fuel pump leaking

Post by adamhut »

thanks for the info and suggestions. I tried first the most simple solution, tightening up the cover screws. They didn't seem loose, but I tightened each of them1/8 turn or less. Started the car up, and surprise...no leaks! :tu: Hope it holds out, and I'll be watching it closely.

really appreciate the quick responses from this forum...
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