Adjustments for 1968 Pontiac Tempest & Firebird 250″ engine.

The Rochester BV carburetor is a one barrel downdraft carburetor with a divorced choke. Divorced meaning the choke thermostat is mounted in the manifold, connected to the carburetor with a choke rod.


Idle Speed & Idle Mixture

Turn the idle mixture screw in (clockwise) until seated, lightly. Scoring of the idle mixture screw is caused by being turned in to hard. Turn the screw back out (counter clockwise) about 5 turns.

  • Bring the engine to operating temperature.
  • With the solenoid engaged adjust the stop screw until the engine is running at 610 rpm.
  • Turn the idle mixture screw in until the engine speed is 600 rpm.
  • Disconnect the stop solenoid so that it is de-energized. The throttle valve will close until the stop screw contacts the low step of the fast idle cam.
  • Adjust the stop screw until the engine reaches the idle speed of 500 rpm.

The fast idle adjustment is not necessary. This setting is adjusted automatically when the above is completed.

Note: A carburetor in need of a rebuild can sometimes be identified by the idle mixture screw not making any difference in engine rpm when being adjusted. A rough idle after doing the above steps can also indicate a dirty carburetor assuming the electrical system is up to par.

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