Rochester Carburetor Tips & Tricks

Written by chris stevenson
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Rochester Carburetor Tips & Tricks
If properly cared for, the Rodchester carburettor can last a lifetime. (American v8 engine image by kenmo from Fotolia.com)

The Rodchester quadrajet has many features that make it a fuel-efficient and altitude-friendly carburettor for the seasoned, high-performance specialist or the owner of one of the classic cars or trucks that spawned from the 60s and 70s. Providing excellent driving performance, it has features that allow for easy tuning and adjustment. The quadrajet came stock on engines, such as the Buick V6 muscle cars and all the way up to the Cadillac V8, which had the 500 cubic inch engine.

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Secondary Throttle Design and Gas Mileage

Due to the unique features of the secondary throttle plates on the quadrajet, when the accelerator activates, the secondary circuit creates an enormous fuel demand. Keep a heavy foot off the accelerator when driving during normal conditions. The primary, smaller throttle plates have more than enough acceleration power to drive the vehicle without ever opening the secondary circuit. Drivers can save on gas cost by using this easy method.

Tube Orifices

The quadrajet has four small tubes that protrude from the air horn. They consist of the secondary air bleeds and the acceleration well tubes. For the purpose of inspection and cleaning, all of the tubes should be clear of any debris or varnish. As they come precisely sized on the inside, no wires should be used to clean them. A strong acidic carburettor cleaner or hot tank immersion remains the proper way to clear the four orifices of any obstructions.

Brass Carburetor Parts

The quadrajet has many brass parts on the inside, like the needle seat. Care should be taken when removing the needle seat with a screwdriver, since it can be damaged by harsh turning force or slippage of the screwdriver. The carburettor float consists entirely of brass parts. The float height (measurement) determines the fuel level in the bowl. Any bent or misaligned part of the brass float levers can change the float level, either starving or flooding the engine. Be careful when working on the float, as these parts have critical alignment parameters.

Primary Power Piston

The springs and metering rods that attach to the primary power piston have been calibrated by the factory. The springs, in particular, should never be stretched or pulled past their tension limits. The bottom spring on the primary valve controls intake manifold vacuum. Overly stretched, the bottom spring can change engine vacuum, which effects the engine performance. Take extra care when cleaning these precision parts, never removing brass with abrasives. Use strong carburettor cleaner and forced air pressure.

Choke Setting

Calibrate the choke setting carefully to factory specifications. By following the sequence for each linkage adjustment in order, you can be sure that the choke, secondary circuit and throttle response will perform precisely, as though if it were new.

Accelerator Pump

The accelerator pump meters fuel under rapid and hard acceleration. The sudden opening of the throttle pushes the pump in a downward direction. The cupped seal sends fuel through the pump jets. Inspect the cupped seal carefully for any brittle spots, nicks or cuts. Even the slightest deformities can cause poor acceleration and stumbling throttle response. More than any other part in the quadrajet system, the cupped seal for the accelerator pump should be replaced upon every inspection or repair.

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