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Hilborn Technical Support - Mechanical - Fuel Injector Manifolds
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Manifold Adjustments

Hex Link Adjustment:
1. Remove injector stacks.
2. Remove all external throttle return springs.
3. Loosen lock nuts and back out idle stop screws on both ends of the injector.
4. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
5. Loosen the allen head pinch clamp screw on only one bronze throttle arm, lightly tap the butterflies on either side of the injector closed with your fingers and tighten the pinch clamp screw.
6. Reinstall throttle return springs.
7. Reinstall injector stacks.

Butterfly Arc Adjustment:
1. Remove injector stacks.
2. Remove all external throttle return springs.
3. Loosen lock nuts and back out idle stop screws on both ends of the injector.
4. Two pieces of round stock are required for gauging. Verify the gauging that you will be using to be within .001 of an inch from each other. Two Philips head screw drivers from the same manufacture or socket extensions are ideal.
5. Insert gauge #1 between throttle blade and wall of injector. While supplying light pressure with your finger to hold the butterfly against the gauge, insert gauge #2 between an open butterfly on the other side of the engine. If gauge #2 has a light drag without opening the butterfly against gauge #1, the arc is correct, proceed to line 6. If gauge #2 is either loose or tight, see the selection below for further adjustments.
6. Remove gauging from the injector.
7. Reinstall throttle return springs.
8. Reinstall injector stacks.

Arc Adjustments:
1. Remove gauging from the injector.
2. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
3. Loosen lock nuts on either side of balance bar. One side of the balance bar will have a groove around the outside of the hex link; this is to identify a left hand thread.
4. If gauge #2 is loose, lengthen the hex link up to a half turn.
5. If gauge #2 is tight, shorten the hex link up to a half turn.
6. Lightly tighten the lock nuts on the hex link.
7. Loosen the allen head pinch clamp screw on only one bronze throttle arm, lightly tap the butterflies on either side of the injector closed with your fingers and tighten the pinch clamp screw.
8. Insert gauge #1 between butterfly and wall of injector. While supplying
light pressure with your finger to hold the butterfly against the gauge, insert gauge #2 between an open butterfly on the other side of the engine. If gauge #2 has a light drag without opening the butter- fly against gauge #1, the arc is correct, proceed to line 10.
9. If gauge #2 is still out of specification, repeat all the steps until correct spacing is accomplished.
10. Without introducing bind in the heim joints, fully tighten hex link lock nuts.
11. Remove gauging from the injector.
12. Reinstall throttle return springs.
13. Reinstall injector stacks.

Centering Butterflies in an Injector:
1. Remove injector stacks.
2. Remove all external throttle return springs.
3. Loosen lock nuts and back out idle stop screws on both ends of the injector.
4. Identify bronze throttle shaft couplers, loosen both allen screws.
5. Identify the hex link that runs to either side of the injector and the bronze throttle arms.
6. Loosen the allen head pinch clamp screw on only one bronze throttle arm.
7. Loosen all the butterfly screws.
8. Lightly tap the butterflies closed with your finger while lightly sliding the throttle shaft back and forth against its stops.
9. Center throttle shaft side to side. Tighten butterfly screws using caution not to over tighten.
10. Tighten both allen screws on bronze throttle shaft coupler.
11. Perform same adjustments on other side of engine.
12. Tighten the pinch clamp screw on bronze throttle arm.
13. Reinstall throttle return springs.
14. Reinstall injector stacks.

Advanced Tuning
Using a temperature gun, identify individual header temperatures. Taking care to check in different locations as different parts of the tube will be different temperatures. Cluster like temperatures together to reduce the amount of tuning required. In other words don’t adjust six cylinders to match two. Higher header temperatures need less air while cooler header temperatures require more air.

Butterfly Adjustments:
1. Remove injector stacks.
2. Remove all external throttle return springs.
3. Loosen lock nuts and back out idle stop screws on both ends of the injector.
4. Open butterflies and identify which end of the blade points up.
5. Mark the up end with a marker. Butterflies are beveled and need to go back in the correct orientation (see Butterfly Installation). Also, adjustments to the butterfly will be done on the end that points up.
6. Remove the two screws and lock washers that hold the throttle blade, taking care not to drop them into the engine.
7. Open throttle shaft to wide open throttle while grasping the end of the throttle blade to remove it.
8. Protect the throttle blade from vise damage by using a piece of aluminum on either side. A rod vise works very well also.
9. Using the throttle shaft witness marks as a guide insert the butterfly between the aluminum lining it up with the witness mark. The end of the butterfly to be adjusted should be sticking out of the vise and both throttle shaft witness marks should be hidden.
10. Lightly tap the blade in the direction required. If the cylinder requires more air, adjust butterfly as to open it in the throttle bore, and conversely, if the cylinder requires less air, adjust butterfly to close it in the bore. Remember that .010 of an inch is a lot.
11. Reinsert butterfly into the throttle shaft. Install butterfly screws, yet leaving loose enough for adjustment.
12. Loosen the allen head pinch clamp screw on only one bronze throttle arm.
13. Loosen all the butterfly screws.
14. Lightly tap the butterflies closed with your finger while lightly sliding the throttle shaft back and forth against its stops.
15. Center throttle shaft side to side. Tighten butterfly screws using caution not to over tighten.
16. Tighten the pinch clamp screw on bronze throttle arm.
17. Reinstall throttle return springs.
18. Reinstall injector stacks.
19. Set idle speed and verify cylinder temperatures. Readjust as required.