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Home >> GMC >> 1982 >> Forward Control 4.8L Eng VIN T, Standard Trans >> Repair and Diagnosis >> Engine Performance >> Tune-Up >> Tune-Up - 6 CYL >> Idle Mixture >> Lean Drop Procedure >> 4.8L Models Only

4.8L Models Only

  1. Set parking brake and block drive wheels. Remove air cleaner for access to carburetor, but keep vacuum hoses connected. Disconnect and plug other hoses if directed on Emission Control Tune-Up decal.
  2. Warm engine to normal operating temperature. Make sure choke is open and air conditioning "OFF". Connect a tachometer to engine. Disconnect and plug distributor vacuum advance hose. Check ignition timing and adjust if necessary. Reconnect vacuum advance hose.
  3. Carefully remove limiter cap from idle mixture screw. Lightly seat mixture screw, then back out just enough so engine will run. Place transmission in neutral.
  4. Back out mixture screw slowly until maximum idle speed is obtained. Adjust idle speed screw so enriched RPM is 0-75 RPM faster than idle speed. Turn mixture screw in until idle RPM is reached. Reconnect all hoses and install air cleaner, then recheck idle speed.
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