How to Adjust a Two-Barrel Rochester Carburetor


The two-barrel Rochester carburetor is designed with two adjustment screws, located in the front of the carburetor near the base. Adjusting the carburetor is fairly simple and the adjustment screws are easy to access. The idle fuel mixture screw on the left side and the idle speed screw on the right side should be adjusted to read the same on the vacuum gauge at the highest readings possible to get the best performance from your engine.

Things You'll Need

  • Screwdriver
  • Vacuum gauge
  • Locate the two idle adjustment screws in the front of the two-barrel Rochester carburetor and turn both screws clockwise with a screwdriver until they are completely closed. Be careful not to over-tighten the screws.

  • Turn the adjustment screws back, counterclockwise one and a half turns with the screwdriver to use as a starting point for your adjustments. Start the engine and let it warm up for about five minutes.

  • Remove the rubber vacuum hose from the base of the carburetor and attach a vacuum gauge to the vacuum port at the base. Start with the idle fuel mixture screw on the left side of the carburetor, looking at it from the front of the vehicle and turn the screw a quarter turn.

  • Turn the idle speed screw on the right side a quarter turn and alternate back and forth, adjusting the screws until you get the highest rpm readings possible on the vacuum gauge with the engine running smoothly. Continue the adjustments, alternating between them until both are reading the same rpm while running smoothly.

  • Adjust both screws one final time by turning them a quarter turn counterclockwise and verify that both are reading the same rpm. Remove the vacuum gauge and reattach the rubber vacuum hose to the vacuum port. Shut the engine off.

Tips & Warnings

  • Be careful of moving engine parts when adjusting the two-barrel Rochester carburetor with the motor running.

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