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.
Carburetor - MOTORCRAFT 740 2-Bbl: Description
Motorcraft Model 740 carburetor is 2-stage dual venturi downdraft type. It has 4 basic metering systems: choke, idle, main metering and acceleration. On some California models with A/T, power enrichment system is also provided in form of power valve. On all other models, power valve has been deleted. Brass plug pressed into power valve channel prevents fuel flow.
All Model 740 carburetors are equipped with idle fuel shutoff solenoid to prevent dieseling. Solenoid, which is energized through ignition switch, opens to allow fuel into idle circuits when ignition is on. When ignition is off, idle fuel shutoff solenoid is deactivated and blocks fuel from idle circuits of carburetor.
Model 740 carburetor uses system of altitude compensation that will operate when vehicle is above 4000 ft. (1220 m). System ceases to operate below 3500 ft (1067 m). Altitude barometric switch allows 12-volt current to energize canister purge (bleed) solenoid. Filtered intake air bleeds into primary idle circuit and into both primary and secondary main circuits to create leaner mixture at higher elevation.
Jet retainer clips are used to keep primary and secondary jets in body of carburetor. Jet clips MUST be installed after any disassembly or jets will vibrate loose from carburetor body. DO NOT use 1981-83 repair kits as later carburetors require smaller holes in bowl cover gasket around idle jet holders.
Idle speed control (ISC) is throttle positioner which uses direct manifold vacuum for control. ISC maintains specified idle speed during engine loading due to A/C operation, power steering effort, electrical loads and friction from new engine components. ISC uses large spring-loaded vacuum diaphragm. When manifold vacuum is low, ISC plunger will move out due to spring pressure and increase throttle plate opening. Plunger is at point of greatest extension when manifold vacuum is at lowest level.
Some models are also equipped with Wide Open Throttle (WOT) A/C cut-out switch to disengage air conditioning compressor clutch during WOT operation.
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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.
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