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Replacement In-Tank Fuel Pumps for Carbureted Vehicles

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					Replacement In-Tank Fuel Pumps for Carbureted Vehicles
Narrative and sketch by Norm Helmkay

These in-tank electric fuel pumps were original equipment for carbureted GM cars with a 3.0 liter and smaller engines.
They will not work for fuel injected cars (pressure too low).


Pump details:
1. AC logo on the inlet end.
2. No strainer sock on the inlet which is about 3/4 inch dia. (Strainer socks available from GM)
3. The outlet pipe fits into a 3/8 inch hose.
4. Outlet end has a removable green plastic terminal block with two spade terminals. The Minus connector spade is a bit
wider than the Positive. This terminal block is attached to the pump with two hex nuts. Some cars have push-on
terminals, use them if you wish, I prefer the security of ring terminals with nuts and washers.
5. Pump diameter 1 3/8 inches, length 4 inches.
6. Fuel pressure at 13.8 volts, 4.5 PSI
7. Delivery volume through a 3/16" pipe at 13.8 volts is a bit less than a quart a minute.

Email me if you have any other questions at corvair@fan.net


Installing An In-Tank Electric Fuel Pump
GM began installing submerged electric fuel pumps in the early seventies. Since then, most auto companies have gone to
an in-tank pump. These AC-Delco pumps are a single stage, rotary pump suitable for carbureted vehicles of 3.0 liters or
less. They deliver close to a quart per minute with 4.5 pounds at 13.8 volts.

There are a couple of reasons for making a conversion to an electric pump, especially for the Corvair. First, is seems
difficult to get a reliable replacement Corvair mechanical pump. The technical giants in the Corvair club have a theory
that modern fuel effects the pump diaphragm, causing it to rupture and fill the crankcase with gasoline. Second, the
aromatic mixtures of modern gasolines tend to vapor lock more easily, especially with the high under-hood temperature of
the Corvair. The electric fuel pump solves this problem by pushing cool fuel through any vaporized fuel in the gas lines.


These instructions were developed primarily for the 1961 to 1969 Corvair, but are applicable with slight modifications to
any vehicle with a 12 volt battery.

Begin by marking the sides of the pump with a Plus (+) and Minus (-) sign before removing the nuts holding the green
terminal block. Cut two pieces of wire, one about 6 inches long (Minus -), the other long enough to reach the top of the
sending unit (Plus +). Crimp or solder small ring connectors on both ends of the wires.

Attach the wires at the pump using the nuts and washers that held on the green terminal block. Make sure the longer wire
is on the Plus (+) terminal.

The in-tank pump is mounted at the end of the fuel pick-up tube, inside the fuel tank. The pick-up tube is usually part of
the sender unit for the gas gauge. This assembly is mounted in the gas tank with a clamping ring. The first step is to drain
the tank and pull the sender assembly.. Often it is much easier to remove the whole tank and work on the unit out of the
car.

Note: Use extreme caution while draining and working around gasoline. Don’t use an incandescent lamp while
working on the fuel system, as any fuel splashed on the hot bulb is easily ignited.

If there is a strainer assembly at the end of pick-up tube it has to be cut off to attach the in-tank pump. This tube also must
be bent to allow the pump to clear the float so it can rest near the bottom of the tank. If you don’t have a spare tanks that
you can cut in two as a model, a way to do this is to make a wire template of the tank shape with a piece of coat-hanger.
This allows the fitting of the assembly along side the wire template before installing it back in the tank.
Next the pick-up tube is cut to position the pump. The exact length is not critical, but leave enough tube for the pump to be
connected with a 2 inch length of 3/8 inch gas-proof rubber hose. (see Fig. A). Secure the pump with compression screw
clamps on either end of the rubber hose.

In addition to making sure the pump does not interfere with the sending unit float, it is also important to make sure the
pump is close to the bottom of the tank. A good idea is to slip a couple of 1 1/4 inch “O” rings over the pump as
bumpers to stop the pump from rattling on the bottom. At this stage, you can trial fit the assembly in the tank. Listen
carefully to hear if the pump taps the bottom.

These pumps can be fitted with a screen sock from GM dealers. There are two varying thought on the in-tank sock. One
group says leave it off and filter outside the tank, the other says the sock protects the pump from jamming with crud off the
inside of a plus 30 year old tank. Take your pick.

An insulated electrical pass-through terminal is already used to connect the gas gauge wire. A second insulated pass-
through is needed to bring the pump wire outside the tank. If you have a spare gas gauge sender, you can liberate the
insulated terminal from it for installation of the pump. Radio Shack sells a nylon insulated binding post (p/n 274-662)
that can be used for this purpose. It mounts in a 5/16" hole. If you are installing the pump in a Corvair tank, the best place
to drill a hole for this connector is on the stamped boss opposite the existing stock connector. After installing the binding
post, check with an ohmmeter to make sure there is no short between the center of the post and the top of the sending unit.
Attach the Plus (+) wire to the bottom of the binding post.

A house-wiring (Romex) aluminum strap with a bolt and nut makes a convenient small clamp (Fig. A side view) to go
around the pick-up tube and provide a connection for the Minus (-) pump wire. Sandpaper the pipe to make a good
electrical ground. Be sure to attach it as low as possible above the rubber connector hose. This keeps it submerged and
away from rust.

On the outside of the tank, if it is hard to attach either the pump or gas gauge wires to their respective connector, bent the
tube slightly so as not to interfere (Fig. B). To make sure the wires don’t interfere with the float. Use some nylon wire ties
to attach the wires to the pipe. Cut off any tie tails. Be sure to test run the pump with a jumper on the top terminal and the
gauge unit grounded before installing in the tank.

Getting power to the pump involves adding a safety switch of some type. GM uses a 3-contact oil pressure switch so the
pump only runs when the ignition is on and the oil pressure is up. For the Corvair, use a from a Chev Vega (you may also
need a couple of 1/8" pipe tees and short nipples if you also have an oil pressure gauge).

These switches are available from most local auto parts stores. Three part numbers: NAPA (Echlin brand) p/n OP-6610 or
Standard brand p/n PS-133 or Delco PS-9. While at the parts store, also get a standard sealed-beam headlight 3-prong
socket connector. This connector fits the new oil pressure safety switch.

There are two ways to connect the oil pressure safety switch depending on if there is an oil pressure gauge or an idiot lamp.
The switch has three prongs marked “I”, “S” and “P.” When there is NO oil pressure, the “S” and “P” are connected.
When there is oil pressure, the “I” and “P” are connected.

In the gauge type installation, (Fig. C) without a priming switch, the “I” wire is connected to the 12 volt side of the
Ignition dropping resistor. The “P” wire goes up to the pump. Only one wire need be run from the back to the front. It is
also a good idea to put a 5 amp fuse in this line. The “S” wire goes to the starter solenoid “S” terminal to energize the
pump during cranking. The negative terminal of the pump is grounded to the pick-up tube with a clamp. (see Fig. A side
view).

In the idiot lamp installation (Fig. D), a pump priming switch should be installed for occasions where the vehicle has been
idle for a long period and the carburetor bowls are dry. The momentary bypass switch is connected between the “I” and
“P” contacts. With the ignition on and the switch pressed, the pump will run to prime the carburetors, before turning the
key to the start position. Other idiot lamp differences are the 12 volt ignition wire is connected to the “P” terminal and the
pump is connected to the “I” terminal. Finally, in the dash, the wire from the oil pressure lamp that normally gets its
power from the common instrument 12 volt supply must be disconnected and grounded.
How does it work?
In the gauge installation, a wire runs from the pick-up terminal of the starter solenoid which is energized only when the
key is turned to start the motor. The current goes through the normally closed (at rest) contacts of the oil pressure switch
to the fuel pump (between contact “S” and contact “P”). When the engine starts and the oil pressure rises, the switch
transfers, causing current flow from the ignition switch (contact “I”) through the transferred switch contacts to the fuel
pump (contact “P”). As long as oil pressure is maintained and the ignition is on, the pump keeps running. This is also an
engine protection feature, if oil pressure is lost from an oil pump failure, the engine automatically shuts down.

Remember, the fuel line to the engine is now under pressure (before it was in suction) so it is important to make sure all
connections are tight, especially if you had an in-line fuel filter in the previous set-up.

In the engine compartment after removing the pump push rod, there are several options:
(A) remove the original mechanical pump completely (recommended) and re-pipe.
(B) bypass the original fuel pump.
(C) alter the old mechanical fuel pump so the fuel passes through it (for the “stock” look).
    Instructions for this method are in the CORSA Tech Guide Fuel-Air Section, page 17.

In route “A,” a plug is needed to fill the hole where the mechanical fuel pump was installed. This plug is easily made from
the old fuel pump. Cut the stem off just below the point where it mushrooms out. File the top of the stem flat and tap the
center hole (where the push rod was) for a 3/8"-16 half inch bolt (same big bolt that holds down the late model top shroud).
Put some oil-proof Loc-Tite on the threads and tighten the bolt in place. Re-install the plug where the fuel pump was
removed. Make sure you don’t damage the “O” ring while making the modification.

In either route “A” or “B” you need to re-pipe around the fuel pump. For safety reasons, rubber fuel hose should not be
used in the engine compartment, remember the fuel is now under pressure where before it was not pressurized until it came
out of the mechanical pump. A simple solution is a short 8" ready-made steel brake line with the inverted flare fittings
already on the pipe. This pipe with a couple of inverted flare couplings safely by-passes the old pump.

The stock fuel pump at 1,000 RPM is supposed to develop a pressure of 4 to 5 pounds, exactly the same as the AC-Delco
in-tank pump. Most carburetors in good condition can handle this pressure easily. However, if the float and needle valves
are not properly set, it may be necessary to add a pressure regulator. The regulator, when installed, goes in the line before
the distribution tee to the carburetors.

The pump operates quite quietly, however, it is a rotary turbine type pump that was designed for a rear mounted gas tank
where it was well muffled from the passenger compartment. Installed in the Corvair, it seldom can be heard over the
engine noise, but at idle, it is a comforting hum.

Many thanks to Blake & Tim Palmer who pioneered this idea and wrote their version in the CORSA Tech Guide (page
22).

				
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