I've posted this before. But, judging from some recent phone calls I've gotten, it must be time to do it again.
I'll compare the operation of the FI unit to a Holley carburator because most Corvette owners are more familiar with carbs. Calibrating an FI unit is much like selecting the jets, power valve, accelerator pump cam, and shooter size for a Holley. Yes, it's that important.
You first "pick the primary jet size" by setting the economy stop. You position the tip of this stop so that the fuel pressure at the nozzle inlet at a certain engine rpm is appropriate for the nozzle size you're running. You do not set this stop, much less the power stop, using a vacuum gauge. You determine the fuel pressure by reading a sensitive pressure gauge hooked directly to a nozzle inlet. Since 100% of the people reading this won't go to the trouble to install any kind of pressure gauge, I'll just stop the discussion of proper procedure right here. Now let's talk about the Monkey / Football Calibration Method for Do-It-Ur-Selfers.
Pre-set the economy stop to project out about 3/8" toward the lever from the casting boss. Let the engine fully warm up. Turn the idle speed screw to hold the engine rpm at 2300 rpm for '57 - '62 units or 2600 for '63 - '65 units. Using a flex-allen tool, rotate the economy stop screw forward and back to determine the highest rpm reading. Moving the stop will probably vary the engine speed about 100 rpm. Leave the stop at the position that gives you the highest rpm reading.
Now position the power stop tip (on the lever end) to be about 1/2" from the tip of the economy stop. Setting the power stop is like picking the right shooter size and secondary jet size for a carb.
You can get out the vacuum gauge now and hook it up to the enrichment diaphragm. Set the length of the enrichment lever rod to allow the lever to leave the economy stop when the vacuum drops below 9" (for 097 cam engines) or 6" (for 30 - 30 cam engines). This is like picking the right accelerator pump cam and power valve for a Holley. NOTE: Despite the urban calibration legend, you do not give a damn about the vacuum gauge reading when the lever reaches the power stop. You only care that it CAN reach the power stop.
If you have a properly calibrated FI unit, you will have a 1/4 to 1/2 turn sensitivity in the idle mixture screw adjustment in BOTH directions at 850 rpm. This means that the engine rpm will dip noticeably when the mixture screw is turned that much either way from the ideal setting.
I will still give phone advice for free if you think I can help you. However, if the terms I've used in the above instructions are confusing to you, my guess is that you're not going to appreciate my advice. I don't talk any smarter than I type. And, if you're using a camshaft, valve lash adjustment, or distributor initial timing that gives you less than a steady 12 inches of manifold vacuum at an 800 rpm idle, then you're wasting your time working on the injection unit. Fix your engine first.
I'll compare the operation of the FI unit to a Holley carburator because most Corvette owners are more familiar with carbs. Calibrating an FI unit is much like selecting the jets, power valve, accelerator pump cam, and shooter size for a Holley. Yes, it's that important.
You first "pick the primary jet size" by setting the economy stop. You position the tip of this stop so that the fuel pressure at the nozzle inlet at a certain engine rpm is appropriate for the nozzle size you're running. You do not set this stop, much less the power stop, using a vacuum gauge. You determine the fuel pressure by reading a sensitive pressure gauge hooked directly to a nozzle inlet. Since 100% of the people reading this won't go to the trouble to install any kind of pressure gauge, I'll just stop the discussion of proper procedure right here. Now let's talk about the Monkey / Football Calibration Method for Do-It-Ur-Selfers.
Pre-set the economy stop to project out about 3/8" toward the lever from the casting boss. Let the engine fully warm up. Turn the idle speed screw to hold the engine rpm at 2300 rpm for '57 - '62 units or 2600 for '63 - '65 units. Using a flex-allen tool, rotate the economy stop screw forward and back to determine the highest rpm reading. Moving the stop will probably vary the engine speed about 100 rpm. Leave the stop at the position that gives you the highest rpm reading.
Now position the power stop tip (on the lever end) to be about 1/2" from the tip of the economy stop. Setting the power stop is like picking the right shooter size and secondary jet size for a carb.
You can get out the vacuum gauge now and hook it up to the enrichment diaphragm. Set the length of the enrichment lever rod to allow the lever to leave the economy stop when the vacuum drops below 9" (for 097 cam engines) or 6" (for 30 - 30 cam engines). This is like picking the right accelerator pump cam and power valve for a Holley. NOTE: Despite the urban calibration legend, you do not give a damn about the vacuum gauge reading when the lever reaches the power stop. You only care that it CAN reach the power stop.
If you have a properly calibrated FI unit, you will have a 1/4 to 1/2 turn sensitivity in the idle mixture screw adjustment in BOTH directions at 850 rpm. This means that the engine rpm will dip noticeably when the mixture screw is turned that much either way from the ideal setting.
I will still give phone advice for free if you think I can help you. However, if the terms I've used in the above instructions are confusing to you, my guess is that you're not going to appreciate my advice. I don't talk any smarter than I type. And, if you're using a camshaft, valve lash adjustment, or distributor initial timing that gives you less than a steady 12 inches of manifold vacuum at an 800 rpm idle, then you're wasting your time working on the injection unit. Fix your engine first.
Comment