Fuel Pump Replacement

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lalkie
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Fuel Pump Replacement

Unread post by lalkie » Tue Sep 12, 2017 6:31 am

I have a 65 corsa and believe the fuel pump is getting weak. I have installed a marine water filter to help with problems associated with ethanol fuel. I have a electric fuel pump and was going to put it in line with the mechanical pump. Is this a good or bad idea? Thanks Larry

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terribleted
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Re: Fuel Pump Replacement

Unread post by terribleted » Tue Sep 12, 2017 10:00 am

If installing an electric pump it is really best to bypass the stock unit. A failed stock pump diaphragm could allow the electric unit to fill the crankcase with fuel unnoticed. The electric pump should deliver 3-5PSI only and should be mounted close to the tank outlet. It is also best to install safety switches such as an inertial switch and low oil pressure shut off to kill the electric pump when the engine is off or in event of a collision.

It would be somewhat unusual for the stock unit to get "weak" why do you think this?
Last edited by terribleted on Tue Sep 12, 2017 10:03 am, edited 1 time in total.
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bbodie52
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Re: Fuel Pump Replacement

Unread post by bbodie52 » Tue Sep 12, 2017 10:02 am

I don't know a valid reason for running both an electric and mechanical pump at the same time. If you believe that the mechanical pump is failing for some reason, you should test it to determine the cause of the apparent failure. The pump should be tested for both output pressure and output volume, as described below. There are possible external causes of a mechanical fuel pump failure that can be easily corrected. The mechanical pump itself may also have an internal defect. Proper troubleshooting techniques can identify the fault and possibly validate the need for a replacement pump. If you decide to install an electric fuel pump, the pump should be installed close to the fuel tank, and not in the engine compartment. Electric fuel pumps do not do a very good job of drawing fuel from long distances. They are better at pressurizing the fuel line from the tank location to the carburetors. Mechanical fuel pumps are good at drawing the fuel from the fuel tank by creating a vacuum in the fuel line between the tank and the pump inlet. A leak anywhere in the fuel feed line (between the tank and the mechanical pump inlet) may not be easily noticeable, because that fuel line is not under pressure. But that same air leak prevents a vacuum from being formed properly to pull the fuel the length of the car to the pump inlet. This can cause the pump to fail to deliver adequate volume to the carburetors. Procedures for checking for this fault and other potential problems are shown below.

If you decide to switch to an electric fuel pump, the pump should be properly mounted in a protected location near the fuel tank, so that gravity will deliver continuous fuel to the pump. A filter near the electric fuel pump inlet will help prevent contaminated fuel from entering the electric fuel pump. Safety switches should be incorporated into the electric wiring circuit to ensure that the pump is turned off if the engine fails. This type of safety switch is designed to provide electricity to the pump when the engine is being cranked, and when the engine is running (using oil pressure to trigger the switch). A loss of oil pressure from the engine will simultaneously cut power to the electric fuel pump. There is also an inertia safety switch that will cause power to be cut to the pump in the event of an accident. Without the proper use of safety switches the electric fuel pump could potentially continue to operate even when the engine has stopped. This could create a fire hazard.

If you decide to switch to an electric fuel pump, Clark's Corvair Parts offers a replacement for the mechanical fuel pump body that provides appropriate passages for the fuel to pass through the existing fuel lines.

:link: http://www.corvair.com/user-cgi/catalog ... IN&page=66
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bbodie52 wrote: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. There was certainly a period of poor quality aftermarket replacement pumps, and 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 and 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 found on turbocharged Corvairs.

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. It is also possible to purchase an aftermarket fuel pressure regulator such as the one shown below.

Here is a link for ordering the recommended Holley fuel pressure regulator...

:link: http://www.jegs.com/i/Holley/510/12-804 ... 1797507184

Holley 12-804 - Holley Fuel Pressure Regulators — $30.41
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Holley#510-12-804

Standard Pressure Regulator
Chrome Finish
For use with gasoline
Port Size: 3/8'' NPT Inlet/Outlet
1 to 4 PSI
Includes Mounting Bracket

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 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! :doh:
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There is also a fuel tank strainer inside the gas tank on the outlet tube. It was listed as a part used in 1960-1965 Corvairs, but it could be installed on any model year. It is conceivable that this strainer could become plugged and could restrict fuel flow to the fuel pump.

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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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:chevy:
Brad Bodie
Lake Chatuge, North Carolina
Image 1966 Corvair Corsa Convertible

lalkie
Posts: 95
Joined: Wed May 29, 2013 11:37 am

Re: Fuel Pump Replacement

Unread post by lalkie » Tue Sep 12, 2017 4:59 pm

I will do some more testing and probably replace it with a mechanical pump as the electric pump sounds like to much work. Thanks for the responses. Larry

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