Tri Power Carb Conversion


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Tri-Power Carburetor Conversion and Linkage Installation
By: Jim Clark

Early engines were adequately supplied with a fuel/air mixture by simple one-barrel carburetors. As displacement increased and cylinders were added the addition of a second barrel to the carburetor met the increased demand. At idle and lower RPM operation a one two-barrel carburetor supplied sufficient fuel/air input for everyday driving operations. However, extra fuel/air was needed when the engine was operating at higher RPM in applications such as racing.

To satisfy this need multi-carb setups were created to supply additional fuel/air in the days when 4-barrel carburetors were not yet available. When the 4-barrel carburetors were introduced they all but eliminated the multi 2-barrel setups because the 4-barrel eliminated the problems of synchronizing linkage by incorporating everything into one package. Multi carb 2-barrel setups still were used in many performance applications for many years though. Especially in racing and hot rod applications.

Now we only see these multi-carb setups on hot rods and nostalgia themed vehicles. This is especially true on what are commonly referred to as alternate engines. Those other than the smallblock Chevy V8 or the new crate motors. Buick Nailheads, Cadillacs, Oldsmobiles, Chrysler Hemis and Y-block Fords are the most popular of these engines.

Most of these multi-carb setups shared a number of things in common. They had one carburetor that was the main carb equipped with a choke and actuated by the throttle linkage. The additional carburetors were tied together by linkage and were actuated by an adjustable link from the main carburetor linkage. The additional carburetors had no choke and only came online when additional demand for fuel/air was indicated.

To illustrate how one of these setups works we have included the following photos that show a Buick Nailhead tri-carb manifold equipped with three Rochester 2-jets. The manifold, carburetor conversion kit and linkage kit are all from Eelco, PO Box 1127, Canby, OR 97013. Additional information about this kit and other kits they have for popular engines is available on their web site www.eelcoequipped.com.


	The Eelco tri-carb kit for the Buick Nailhead V8 that we are showing in this setup consists of: 3-Rochester 2-jets, 3 longer butterfly shafts, 2 accelerator pump actuators, jets, fuel inlets, choke butterfly-shaft-hole plugs, 2 center-carburetor idle adjustment screws, stainless screw kits and progressive linkage assembly.


	- Base of each carburetor is removed. Original butterflys are removed, new extended shaft installed, then butterflys replaced taking care to reassemble them exactly as when removed. Black arrows on carburetor base show where idle circuit passages on the end carburetors are plugged with Permatex liquid solder. Original shaft and linkage assembly is shown at the left.


	Choke assemblies including the shaft, butterfly and actuator are removed from the end carburetors and plugs inserted into the holes left by removing the shafts. Accelerator pump linkage actuator supplied in the kit is bolted onto the end of the butterfly shaft of each end carburetor


	- Right side view of the carburetor shows the new fuel inlet fitting, longer butterfly shaft and the plug in the hole where the choke butterfly shaft was removed


	To install the longer butterfly shaft in the center carburetor base the shaft is removed and the end of the shaft is sanded or filed until the throttle arm/idle screw assembly can be removed. The new longer shaft is then bolted to this assembly after the hole is dressed


	- An Edelbrock electric choke assembly was added on the center carburetor. Longer butterfly shaft is shown extending from the right side of the carburetor base. Stainless top hold-down screws are shown installed in the top of the carburetor.


	Left side of the Nailhead Buick tri-carb setup shows the new accelerator pump actuating linkage installed on both end carburetors and original linkage actuator installed on the center carb shaft. This is where the throttle linkage connects and idle speed is adjusted

- Extended butterfly shafts allow the progressive carburetor actuating linkage to be installed on the right side where clearance is better. The end carburetors are tied together by the rod at the bottom synchronizing their movement. The actuating arm on the center carburetor shaft pulls the rod opening the butterflys on the end carburetors when the throttle has opened the preset amount. That point is set by moving the locking collar at the far right end of the rod. Collar on the opposite side of the rod closes the butterflys on the end carburetors. A buffering spring is located between the collar and pivot to maintain tension and assure closure of the end carburetor butterflys


	When the throttle is actuated on the center carburetor it pulls the progressive linkage rod back opening the butterflys on the end carburetors. Timing when they open is controlled by adjusting the collar on the end of the rod at the right

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