Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1980FORWARD CONTROL 5.7L ENG VIN M, AUTOMATIC TRANS, TRANS MFR CD 400/M40REPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE MECHANICALFUEL SYSTEMROCHESTER M4MC 4-BARRELOVERHAULDISASSEMBLYAIR HORN REMOVAL
1980 Chevrolet Forward Control 5.7L Eng VIN M, Automatic Trans, Trans Mfr CD 400/M40
Air Horn Removal
1980 Chevrolet Forward Control 5.7L Eng VIN M, Automatic Trans, Trans Mfr CD 400/M40SECTION Air Horn Removal
- Remove upper choke lever from end of choke shaft by removing retaining screw. Then rotate upper choke lever to remove choke rod from slot in lever. Remove choke rod from lower lever inside float bowl casting.NOTE: Remove rod by holding lower lever outward with small screwdriver and twisting rod counterclockwise.
- Remove vacuum hose from front vacuum break unit. Remove secondary metering rods by removing the small screw in top of metering rod hanger. Lift upward on metering rod hanger until secondary metering rods are completely out of air horn. Metering rods may be disassembled from hanger by rotating ends out of holes in end of hanger.
- Drive pump lever pivot pin inward until pump lever can be removed, then disconnect pump rod from pump lever. Remove air horn-to-float bowl attaching screws. Remove secondary air baffle deflector rom beneath center 2 air horn screws. Remove air horn from float bowl by lifting straight up.
- Remove front vacuum break attaching screws and front vacuum break diaphragm. Disconnect diaphragm from air valve dashpot rod and remove dashpot rod from air valve lever.
- It is not necessary to remove choke valve and shaft unless bent or damaged. Choke valve screws are staked in place. Staking must be removed before screws are removed.NOTE: Air horn should not be disassembled any further. Air valve screws are permanently staked in place. However, a repair kit is available for air valve closing spring and center plastic eccentric cam.
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.