Rebuild Video Series (Quadrajet)
Rebuilding Manual (Rochester Quadrajet)
Adjustments (Rochester Quadrajet)
Rochester Quadrajet Carburetor Manual
Exploded Views and Diagrams (Quadrajet)
Metering Circuit (Rochester Quadrajet)
Power Circuit (Rochester Quadrajet)
Accelerator Pump Circuit (Quadrajet)
Choke Pulloffs (Vacuum diaphragms)
Throttle Position Sensor (Quadrajet)
All the various tubes (Quadrajet)
Hot Idle Compensator (Quadrajet)
Air Valve Dash Pots (Rochester Quadrajet)
Idle Vent Valve (Rochester Quadrajet)
Crash course in Quadrajet troubleshooting
Fuel dribbling from venturi (Quadrajet)
No vacuum at one of the ports (Quadrajet)
Lack of power at high speed (Quadrajet)
4MV Diagnosis Chart (Rochester Quadrajet)
There are three basic carburetor models, the 4M, 4M, and 4MV. Except for the variation in choke mechanism, these three models are basically the same.
4M = manual choke operation
4MC = automatic choke carburetor with the choke housing and coil mounted at the side of the float bowl
4MV = automatic choke model designed for use with a manifold mounted thermostatic choke coil
The Quadrajet is a four-barrel, two-stage cabruretor of down-draft design. Its simplicity in contruction makes it easy to service, yet its versatility and principles of operation make it adaptable from small to very large engines, without major casting changes.
The Quadrajet carburetor has two stages in operation. The primary (fuel inlet) side has small 1 3/8" bores with a triple venturi set-up equipped with plain tube nozzles. Operation is similar to most carburetors using the venturi principle. The triple venturi stack up, plus the small primary bores, result in more stable and finer fuel control during idle and part throttle operation. During off-idle and part throttle operation, fuel metering is accomplished with tapered metering rods, operating in specially designed jets positioned by a manifold vacuum responsive piston.
The secondary side of the Quadrajet has two large (2 1/4") bores. These, added to the primary, give enough air capacity to meet most engine requirements. The air valve is used in the secondary side for metering control and supplements the primary bores to meet air and fuel mixture requirements of the engine.
The secondary air valve mechanically operates tapered metering rods with move in orifice plates, thereby controlling fuel flow from the secondary nozzles in direct proportion to air flowing through the secondary bores.
The float bowl is centrally located to avoid problems of fuel spillage causing engine turn cutout and delayed fuel flow to the carburetor bores. The float bowl reservoir is small in design to reduce fuel evaporation loss during engine 'shutdown' hot.
The float system has a single pontoon float and fuel valve for simplification and ease in servicing. An integral fuel filter, if used, located in the float bowl ahed of the float needle valve, is easily removed for cleaning or replacemnet.
The throttle body is aluminum to reduce overall weight and improve heat conduction to prevent icing. A heat insulator gasket is used between the throttl ebody and bowl to prevent fuel percolation in the float bowl.
Early Quadrajet applications use a shim between the throttle body and flange gasket. The shim is used to protect the carburetor aluminum throttle body from exhaust gases flowing through the heat cross-over passage in the intake manifold.