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Home >> Chevrolet >> 1968 >> Chevy II 2.5L Eng >> Repair and Diagnosis (Single Page) >> Engine Performance >> Tune-Up >> Exhaust Emission Systems - Tune-Up >> Idle Speed & Mixture Adjustment >> All Models (Exc. Corvette), 396"/350 HP, 454"/345 HP, 454"/360 HP & 390 HP (1970)

All Models (Exc. Corvette), 396"/350 HP, 454"/345 HP, 454"/360 HP & 390 HP (1970)

  1. Disconnect and plug distributor vacuum advance line. Turn mixture screws in (clockwise) until lightly seated, then back screws out (counterclockwise) four turns.
  2. Adjust carburetor idle screw to obtain 630 RPM with automatic transmission in "D" position. Adjust mixture screws equally to achieve 600 RPM in "D" position.
  3. With manual transmission in Neutral, adjust carburetor idle speed screw to obtain 700 RPM. Turn one mixture screw in (clockwise) until idle speed drops 40 RPM. Regain 700 RPM idle by readjusting carburetor idle speed screw. Turn in other mixture screw until idle speed again drops 40 RPM. Regain 700 RPM by adjusting carburetor idle speed screw.
  4. Reconnect distributor vacuum advance line on both automatic transmission and manual transmission vehicles.
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