Hilborn Fuel Injectors

Technical Support - Mechanical Systems - General Installation
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Installation Instructions

Fuel Injector 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.