Hilborn EFI and MFI Manifold Installation

Author: Hilborn | 11/17/2018 < Back to Motor Life Home

Hilborn Electronic Fuel Injection

The information below is provided to help in the installation of your injector. If you have any questions or problems during your installation, please call the EFI tech line at 215-643-4607.

It is important to design the throttle linkage and the return spring assemblies so they both pull from the same point on the throttle shaft. This point should also be right next to one of the throttle stops. Failure to do so WILL result in poor idle and throttle tip in performance.

Braided lines

All braided lines need to be thoroughly flushed after assembly. The use of a hacksaw, cutoff wheel, etc. creates a tremendous amount of debris, therefore the use of a braided steel hose cutter is recommended.

Injector installation (3-piece models)

  1. Trial fit injector and plate assembly (Use Silicone for the end rail gaskets)
  2. Glue intake gaskets to head and trim gasket if required
  3. Install one half of the injector and torque to spec
  4. Lay a large bead of silicone on all 4 edges of the lifter valley plate (gluing the plate will ensure that the bead of silicone stays below the surface of the plate while providing a good seal)
  5. With a helper, hold the lifter valley plate in place without touching the previously installed injector half and the engine. Slightly tilt up the plate to allow room for the other injector half to slide down onto the head
  6. Together, slide the injector half and the plate down to their final resting place
  7. Torque injector to spec and tighten lifter valley plate screws

BBC additional instructions

All oval ports will require the use of a rectangular port intake gasket such as FelPro #1275. BBC applications require the lifter rails to be drilled and tapped to accept (2) 1/4-20 screws to mount center plate.

351W additional instructions

Engines with the three piece 351 injector require the lifter rails to be drilled and tapped to accept (4) 10-24X3/4 screws to mount center plate

348/409 additional instructions

348/409 Distributor Installed Height: Oil pump tang engagement and distributor gear engagement must be verified using the supplied distributor adapter. If required, this adapter can be machined to set distributor height and is o-ringed for a leak free seal.

348/409 Valley Plate Installation: Due to the unique design of the lifter valley rail, additional sealant will be required on the left rear corner of the valley plate to ensure a leak free installation. 348/409 applications will also require the lifter rails to be drilled and tapped to accept (2) 1/4-20 screws to mount center plate.

Throttle Return Springs

Due to the possibility of twisting the butterfly shafts and/or causing drivability concerns, it is recommended that throttle return springs be attached to the throttle arm or a secondary throttle arm that is mounted next to the throttle arm. A throttle stop should be positioned next to the throttle arm to eliminate shaft twist from the return springs. Return springs are not supplied by Hilborn.

Idle Speed

Idle speed is adjusted using the idle stop screws on either side of the injector. Which screw to use to set the adjustment depends on where the throttle linkage/return spring is located. It is recommended that the idle screw positioned next to the throttle linkage/return spring be used as the main idle adjustment. The secondary stop is correctly adjusted when light return pressure is applied by hand to the throttle stop and the throttle blades only slightly move.


Throttle arms are provided as a means to attach your vehicles linkage or cable to the injector. Brackets may need to be constructed. When constructing your linkage please remember:

  • Cable linkage, such as those available from Lokar Products, provide the greatest flexibility
  • There should not be any bind in your linkage system
  • A mechanical throttle stop should be used; Do not use the injector as the stop or damage to the shafts and couplers could result
  • It is recommended that the throttle return spring be attached to the same point on the injector as the throttle linkage
  • Avoid using the hex link as it is needed for adjustment
  • Throttle shafts and couplers can be easily bent and care should be taken not to introduce twist into these assemblies; Design your linkage placement and return spring arrangements accordingly

Vacuum Kit

On naturally aspirated applications the vacuum kit is comprised of the rubber lines attached to a block mounted in the center of the fuel injector assembly/manifold. A -6 AN fitting is provided to supply vacuum to those accessories that require it. A PCV valve is not recommended. For blown applications, a single -6 fitting is provided. Do not attach a fuel line to the vacuum nipple.


Hilborn Injectors are supplied with (2) -8 nipples for coolant flow out of the engine. These nipples must be positioned at the front of the engine or engine damage may result. If additional coolant flow is required, larger nipples may be substituted. Additional nipples may be added to the rear holes of the injector to help cool the rear of the engine. When using a remote thermostat housing, a 1/8 hole should be put in the flange of the thermostat to allow air pockets to exit.


Magnetos are not compatible with EFI due to electromagnetic interference (EMI). If a magneto is desired, consult your magneto manufacturer for electronic conversions.


In order to keep the battery in a fully charged state it is recommended that the alternator output wire be attached directly to the battery. This will keep voltage drops to a minimum allowing the full potential of the alternator to be used. A minimum of an 8 gauge wire is recommended.

One wire alternators produce a large amount of ripple, therefore it is highly recommended that the output be attached directly to the battery to provide adequate buffering of the ripple.

Hilborn Mechanical Fuel Injection

Fuel Injection Installation and Idle Adjustment

The Hilborn fuel injector is completely assembled, flow tested, and ready to install. The idle mixture and idle speed are factory set but will probably require some adjusting. The idle speed is adjustable by loosening the locknut on the throttle stop screw and turning the screw to open or close the throttle. The idle mixture is controlled at the fuel metering valve on the injector. The linkage between the valve and the throttle shaft consists of a threaded turnbuckle, one end has a right-hand thread and the other has a left-hand thread. Loosen both locknuts and turn the turnbuckle. To richen the idle, adjust the turnbuckle so that the arm on the metering valve moves in the open throttle direction. To lean the idle, reverse the procedure; one half to one turn should be ample. Retighten the locknuts. As previously stated, this adjustment is factory set and need not be tampered with excessively. On models where the injector consists of two castings, fasten the castings to the heads and then adjust the length of the hex linkage rod that connects them together until both throttles are closed down on the throttle stops. This is very important to obtain a good idle and should be repeated with the engine running. Another way is to loosen the allen screw on one of the arms of the cross link, move both throttle shafts to the closed position and tighten the allen screw.

Butterfly Adjustment

Install the injector and the fuel pump onto the engine. If the throttle shows any sign of sticking, loosen all the butterfly screws and tap the shaft back and forth, then all the way to one side. Tap halfway back to center to relocate the line and re tighten the screws. Adjust the butterflies when the engine is hot, except when running methanol, adjust them when the engine is cold. Use thin intake gaskets where possible since thick gaskets may cause the throttles to stick.

Mixture Control

The main mixture control is the jet inside the by-pass container, the #4 By-Pass Valve. To change the mixture, unscrew the cap from the container, and change the jet in the cavity in the cap. Increasing the size of the jet leans the mixture. This container also includes a 4-sided poppet valve and a spring. If the poppet is removed, be sure it is replaced with the pointed end away from the spring and toward the pump. Operating fuel pressures and recommended jet sizes are approximate starting points only. These pressure readings will be attained only at 6000 RPM and with the throttle fully opened. Do not hesitate to use other jet sizes when conditions warrant.

Fuel Filter

Do not, under any condition, attempt to run the engine without installing a high quality fuel filter. We strongly recommend the screen type filters and advise against using paper, ceramic, or laminated metal filters. HILBORN manufactures several types of screen filters. The filter may be mounted anywhere on the intake side of the pump. In addition to the fuel filter, a safety screen is also incorporated into each of the individual injection nozzles to catch any stray particles of dirt. These screens may be cleaned by removing the nozzles and blowing out any foreign material, however, care should be taken to avoid puncturing the screens.

Starting the Engine

Since this is a pressure system, it is necessary to have some degree of fuel pressure to start the engine. If pushing or towing the car is employed, sufficient pressure will be obtained and starting will be no different than with a carburetor. However, it may be necessary to prime the engine when using a starter. If an electric pump is used, do not install it in the main line running between the fuel tank and injector pump since the capacity of these pumps is too small for fuel to pass through. Hook the electric pump on a side branch line discharging into the injector pump outlet line. Very little pressure is required…. just enough to start the fuel dripping from the nozzles will give a quick start. Hold the throttle fully open while priming and then close it COMPLETELY SHUT during the actual starting operation. This eliminates the risk of fire. After the engine is running strong, shut off the electric pump if one is used. Once the engine has been running, the fuel lines will be filled and this procedure probably will not be necessary on any of the succeeding starts. However, for a fast, sure start, it is recommended. On all starts, hold the throttle fully open for a few seconds while the engine is turning, then switch on the ignition. This facilitates bleeding the air from the system. If the fuel pump is mounted below the fuel tank level, it will be primed automatically.

Ram Tubes

We strongly recommend the use of ram tubes on all models of our injectors. Horsepower gains of about 5% to 10% are average for a system with ram tubes. Hilborn stocks a variety of styles in many I.D. sizes and lengths.

Fuel Pump Installation

All Hilborn fuel pumps have grease packed bearings so no additional lubrication is required. We recommend the following inlet hose sizes for fuel pump installations. Do not use smaller sizes. Pump Model PG250, size #5 use 1-1/4″ hose. Pump Model PG175B, sizes #2, #4 use 1″ hose. Pump Models PG150C & PG150D, size #1 use 3/4″ hose. Pump Models PG150C & PG150D, sizes #S0, #0, #00 use 1/2″ hose

Fuel Pump Rotation

To change the rotation of the pump, remove cover bolts and dowel pin. Move the pin 180 degrees to the opposite hole and replace the lid. CAUTION: Sometimes this change results in a tight pump. If so, do not attempt to run the pump! We recommend that it be returned to our factory for correction.

CAUTION: Avoid corrosion on magnesium castings: Many of the HILBORN fuel injectors are designed with magnesium castings. Due to the very reactive nature of magnesium in the presence of water or methanol, we highly recommend special attention to these units. At the end of each race day, remove the nozzles and blow out the nozzle cavity and passageway with air to thoroughly remove any liquids. DO NOT allow liquids to stand in the injector overnight. Failure to keep the casting dry may lead to corrosion! After operating the engine on fuel containing any of the nitro-paraffin series such as nitro methane, flush the entire fuel system with a mixture of gasoline and oil. Do not allow these fuels to stand in the injector overnight as they are damaging to rubber.

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