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Home >> Ford >> 1978 >> Pinto Pony, 2D Sedan, Standard Trans >> Repair and Diagnosis >> Engine Performance >> Engine Control Systems >> Feedback Carb. System >> Carburetor Feedback Diaphragm Assembly
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Carburetor Feedback Diaphragm Assembly

  1. With engine off, disconnect vacuum hose between Vacuum Solenoid Regulator (VSR) and carburetor. Using an external vacuum source, apply 10 in. Hg vacuum to hose and check for leakage.
  2. If vacuum falls from 10 in. Hg to 7 in. Hg within 15 seconds, disconnect hose and apply vacuum directly to carburetor. If leakage rate exceeds specification, go to next step. Otherwise, replace vacuum hose, recheck leakage rate and go to step  7).
  3. Seal feedback system diapraghm adjustment screw with finger and recheck leak rate. See Figure. If leak rate now falls within specified limits, pry open lead plug on adjustment screw.
  4. Apply locking compound to housing threads at leaking screw, let dry and recheck leak rate. If leak rate now falls within specified limits, install new lead plug and go to step  7) If not, go to next step.
  5. Disassemble air horn and remove float assembly. Check for proper torque on feedback system diaphragm assembly cover screw. If torque is 4-5 INCH lbs., go to next step. If not, tighten screw to specified limits and recheck leak rate. If leak rate now falls; within specified limits, go to step  7) Otherwise, go to next step.
  6. Remove diapraghm assembly cover screws. Examine sealing surface for burrs, nicks or other damage. Repair or clean as' necessary. If sealing surface is questionable, reinstall original I diaphragm assembly and recheck leak rate. If leak rate is now correct, go to next step. If excessive leakage still exists, replace carburetor assembly.
  7. While applying 5 in. Hg vacuum to feedback diaphragm vacuum source, observe diaphragm assembly stem for movement. Total stroke must be 0.09" in as vacuum is applied. If not, replace diaphragm assembly as necessary.
  8. Also check feedback system metering needle located at bottom of fuel bowl for free movement. Total stroke from the free to the fully depressed position must be 0.20". If not, repair or replace metering needle as necessary.
  9. After repairs, reassemble float assembly and install air horn on carburetor. If a new diaphragm assembly has been installed, reset idle fuel mixture.
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