Quadrajet Metering Rod

The main metering system (Figure 9) supplies fuel to the engine from off-idle to wide-open throttle. The primary bores (two smaller bores) supply fuel and air during this range through plain tube nozzles and the venturi principle.

The multiple venturis in each primary bore produce excellent fuel metering control due to their sensitivity to air flow.

The main metering system begins to operate as air flow increases through the venturi system and additional fuel is needed to supply the correct air/fuel mixture to the engine. Fuel from the idle system gradually diminishes as the lower pressures are now in the venturi system.

The main metering system consists of main metering jets, vacuum operated primary metering rods, main fuel wells, main well air bleeds, main discharge nozzles, triple venturi, fuel pull-over enrichment (some applications), adjustable part throttle (some applications).

As the primary throttle valves are opened beyond the off-idle range allowing more air to enter the engine intake manifold, air velocity increases in the carburetor venturi. This causes a drop in pressure in the large venturi which increases many times in the boost venturi. Since the low pressure (vacuum) is now in the smallest boost venturi, fuel flows from the main discharge nozzle as follows:

Fuel from the float bowl flows through the main metering jets into the main fuel wells. It passes upward in the main well and is bled with air by an air bleed located at the top of well. The fuel is further bled air through calibrated air bleeds located near the top of the well in the carburetor bores. The fuel mixture then passes from the main well through the main discharge nozzles into the boost venturi. At the boost venturi, the fuel mixture then combines with the air entering the engine through the carburetor bores. It then passes as a combustible mixture through the intake manifold and on into the engine cylinders. The main metering system is calibrated by tapered and stepped metering rods operating in the main metering jet and also through the main well air bleeds.

During cruising speeds and light engine loads, manifold vacuum is high. In this period, the engine will run on leaner mixtures than required during heavy loads. The primary main metering rods are connected to a vacuum responsive piston which operates against spring tension. Engine manifold vacuum is supplied to a power piston through a vacuum channel. When the vacuum is high, the piston is held downward against spring tension and the larger diameter of the metering rod is in the main metering jet orifice. This results in leaner fuel mixtures for economy operation. As engine load increases and engine manifold vacuum drops, spring pressure acting on the power piston overcomes the vacuum pull and gradually lifts the metering rods partially out of the main metering jets. This enriches the fuel mixture enough to give the desired power required to overcome the added load.

When installing the metering rod assembly. Move the rods around until they fall into the main jets. This takes a little patience but don’t force it. They bend easy.

Once down tap the plastic retainer into the recess. This is what will keep the metering rod assembly down. It must move up and down easily. If the retainer fits too loose, stake the sides a bit.

Q-Jet /DualJet Primary Metering Rods

Part Number	Rod Stamping		Part Number	Rod Stamping		Part Number	Rod Stamping		Part Number	Rod Stamping
7034832	32B		7043530	30J		17051340	40K		17056948	48M
7034833	33B		7043536	36J		17051341	41K		17056949	49M
7034834	34B		7043538	38J		17051342	42K		17056950	50M
7034836	36B		7043540	40J		17051343	43K		17056951	51M
7034837	37B		7043541	41J		17051344	44K		17056952	52M
7034838	38B		7043542	42J		17051345	45K		17056953	53M
7034839	39B		7043543	43J		17051346	46K		17056955	55M
7034840	40B		7043544	44J		17051347	47K		17057742	42P
7034841	41B		7043545	45J		17051348	48K		17057744	51M
7034842	42B		7043546	46J		17051349	49K		17057745	45P
7034843	43B		7043549	49J		17051350	50K		17057746	46P
7034844	44B		7046338	50D		17051351	51K		17057747	47P
7034845	45B		7047905	49C		17051352	52K		17057748	48P
7034846	46B		7047906	51C		17051353	53K		17057749	49P
7034847	47B		7047907	53C		17052230	49E		17057750	50P
7034848	48B		7048742	44C		17053334	34L		17057751	51P
7034849	49B		7048743	45C		17053338	38L		17057752	52P
7034850	50B		7048745	47C		17053342	42L		17057753	53P
7034851	51B		7049942	42C		17053343	43L		17057754	54P
7040700	50C		17050099	53E		17053345	45L		17057755	55P
7040701	52C		17051338	38K		17053346	46L		17057757	57P
			17051339	39K		17056358	58P
						17056363	63P