• It is always wise to disconnect the negative cable at the battery before removing a carburetor.
  • Before disconnecting fuel lines, make sure you have planned to have something available to plug the line to prevent gasoline spills.
  • Also, carefully lift the carburetor up and away from the engine. It will have gasoline in it. Keeping it up will prevent spills.
  • The carburetor may also have coolant hoses connected to it.
  • These hoses should also be plugged after they are removed.
  • It is a good idea to drain the coolant from the hoses before totally disconnecting them.
  • Also, as you disconnect vacuum hoses from the carburetor, mark them so you can reinstall them in the same place when putting the carburetor back on.
  • If a spacer is positioned between the carburetor and the intake manifold, replace it with a new one.
  • Also, make sure the sealing surface of the intake manifold is clean and free of nicks.
  • Make sure all adjustments are made to the internal parts of the carburetor before reinstalling it on the intake manifold.
  • Tighten all bolts and screws to the specified tightness, and use new gaskets and seals.
  • When tightening the carburetor to the intake manifold, make sure you tighten the bolts evenly.
  • It is best to stagger the tightening sequence. Doing this will prevent carburetor base warpage and will allow for a good seal.

Idle Adjustment Using Propane Enrichment Method

By the mid-1970s, the combination of catalytic converters and very lean mixtures made it difficult to properly perform curb-idle-speed and mixture adjustments. However, these adjustments must be properly made to ensure that emission control devices limit CO, HC, and NOx to the specified levels. The solution was to use propane gas to assist in achieving correct idle settings. By allowing propane into the intake air, the mixture becomes very rich. Normally engine speed will increase when it is enriched until it has a mixture that is too rich. At this point, the engine speed will decrease. Adjusting the idle mixture and idle speed with the propane allows for a good balance between throttle opening and mixture.

The exact procedure for doing this will vary depending on the vehicle's make and year.

  • Always follow the idle mixture adjustment procedure in the vehicle manufacturer's service manual.
  • On some feedback carburetors, it is possible to adjust the air/fuel mixture.
  • Many manufacturers recommend using a propane enrichment tool to set the mixture on feedback carburetors. On others, this is accomplished entirely by the powertrain control module (PCM).
  • Incorrect air/fuel ratios will cause improper idle speeds or rough idle, as well as high emissions.
  • Feedback carburetors that allow for air/fuel adjustments normally have a concealment plug over the mixture screws.
  • The manufacturer has installed these plugs to prevent tampering with the mixture.
  • If it is necessary to adjust the mixture, the plugs must be removed.
  • To remove the plugs, center-punch the carburetor casting 1/4 in. (6.35 mm) from the end of the mixture screw housing.
  • Then drill the outer housing at the center-punched location with a 3/16 in.- (4.762-mm) drill bit.
  • Pry out the concealment plug and save it for reinstallation.