Subscribe to a magazine

Rebuilding the Carter-Type Flathead WO

P72590 Image Large
Posted November 1, 1999

It's a Snap to Cure This Carb

Step By Step

View Photo Gallery
  • After taking off the carburetor air horn, remove the external choke linkage by loosening the clamp shown. The inner cable wire is set-screwed on and needs to be loosened for removal. Remove the fuel inlet tube, being careful not to strip or break off the fitting.

  • The throttle cable and housing is removed next. The housing is clamped to the carb, and the inner wire hooks to the base of the throttle lever with this set nut. Next, take off the throttle rod after removing the cotter pin.

  • With the carb off, carefully take the atom- izer plate off. This is used to atomize the fuel for better fuel economy and smoother running. Clean the manifold and cover the hole with a rag to prevent debris from entering.

  • One screw holds the top throttle and choke linkages on. Remove the screw and slide the linkage off the bottom throttle linkage.

  • Remove the two screws holding the top air horn to the carb. This exposes the accelerator pump and metering rod linkages.

  • Unfasten the clip at the base of the accelerator pump linkage. Swing the rod up and slide it out of the top linkage.

  • Take out the four top screws and lift the cover straight up. This holds the float with its needle and seat, the accelerator pump, and the metering rod.

  • Use needle-nose pliers to take the clip off the post, then release the small hairspring. Pull the metering rod out and be careful not to lose the small fiber washer that seals the rod to the base.

  • Pull the pin that holds the float in place and remove the float. Take the needle out of the seat, and use a large-blade screwdriver to remove the seat. Take off the gasket and set it aside.

  • Remove the small C-link from the plunger, and remove the plunger and then the linkage. Place all the parts except the rubber and fiber ones in solvent for cleaning.

  • The accelerator pump well has a spring in it. Take the spring out and set in the cleaning solution.

  • The main jet is located in the bottom of the bowl. Use a large-blade screwdriver to unscrew it. Be careful not to damage the jet with the screwdriver, since new jets aren’t available.

  • There are five cover plugs on the exterior that need to be removed for access to the various fuel circuits. Use the appropriate-size screwdriver to prevent damage. Remove and clean all the plugs and replace the fiber washers on them.

  • Some circuits have two items in the same hole. This is the accelerator pump check valve and the accelerator pump discharge check valve. Make sure that they’re kept separate so they’re installed correctly.

  • Remove each jet or nozzle and note where each came from. Some of the openings are so narrow you may have to grind the sides of the screwdriver so it will clear the body.

  • Two big screws hold the carb bowl to the base. Remove the screws and separate the two, being careful not to crack the thin spacer between them.

  • The idle-mixture screw has a spring around it for tension; remove it from the base. The throttle shaft and linkage can be left intact, since service parts aren’t available. If the bore needs to have bushings installed, take it to a good machine shop to have that done.

  • Soak all of the metal parts in a carburetor solvent as shown. Leave the parts in the bucket long enough to thoroughly clean all of the foreign deposits from the metal.

  • After rinsing the solvent from the parts, blow air through all of the holes in the body and jets. Assembly of the carb is the reverse of taking it apart. Use the new parts in the kit. Use new gaskets on each side of the spacer plate and assemble the base to the bowl.

  • Install each jet in its proper location, then use compressed air or carb cleaner to ensure that each passageway is clear. Wear eye protection and be careful of flying debris. Cap off each hole with the proper plug fitted with a new washer.

  • Screw the new seat into the top cover with the proper-size screwdriver. Install the gasket and the needle valve.

  • Install the pin that retains the float, and use the supplied gauge to measure the float level. Bend the arm of the float to adjust the level to the specs given on the instruction sheet. Never press the float down to adjust, since the rubber tip of the valve can be easily damaged.

  • Slide the linkage mechanism into place, and install the new accelerator pump plunger. Install the assembly onto the carb bowl, and tighten the four screws.

  • Most carb kits come with a metering rod adjustment tool, which looks like a simple brass rod. Insert the rod into the metering rod hole on the cover. With the rod resting in the main jet in the bowl, adjust the shoulder of the small nut so that it just touches the rod (arrow).

  • Slide the tool out of the hole, and carefully insert the metering rod, placing the eye over the shoulder. Retain the rod with the hairspring and special clip.

  • Hook the accelerator link to the top mechanism and swing it down to clip into the bottom levers. Install the top of the carb, and tighten the two screws.

  • The idle-speed-adjustment screw should be turned in until the throttle plates barely close in the bore. Install the carburetor and hook up the throttle and choke linkage and the fuel inlet tube. Fire up the engine and adjust the idle-mixture screw until the engine runs smoothly, about two or three turns out. Install the air horn on top, and you’re done.

High idle, low idle, or just a bad bog when you step on the gas, these problems are carburetor kinks that often can be easily fixed. Carburetors are marvelous little devices that mix air and fuel in the proper ratio and deliver it to the engine. Though many Jeeps have fuel injection, the lowly carb still has its place in the Jeep world: It’s simple and reliable. Most carbs have no wires or computers to break or mysteriously fail, and field fixes are relatively easy should the need arise.

Our subject for this story is the original Carter-type WO, a single-barrel downdraft design that powered most Jeep flat-head four-cylinder engines from 1941 through the mid-’60s. The usual tag number is 636, with a variety of letters after the number. The carb shown is a 636SA and was installed on a ’48 CJ2A that hadn’t run in about 10 years. After a minor dusting of the carb and gasing the Jeep, the engine came to life, but it would only idle. Our local auto parts store came up with a rebuild kit for the carb, and we tore into the little bugger to show you how easy it is to rebuild.