General Tune-Up Items and Approximate Ranges:
* Spark Plugs: Generally, AC, Champion, or Autolite plugs were used. The heat range and gap would be specified in your owner's manual, but a range of heat range 8-10 and a gap of 0.035" to 0.045" inches is a common starting point. Always check your owner's manual. Incorrect heat range can lead to pre-ignition or fouling.
* Ignition Timing: This is highly dependent on the engine code and distributor advance mechanism. Initial timing is typically set between 8° and 12° BTDC (Before Top Dead Center) at idle. The total advance (initial plus mechanical and vacuum advance) will be significantly higher, usually between 32° and 38° BTDC. A timing light is essential for accurate setting, and you absolutely need the proper specification from your owner's manual or a Pontiac-specific repair manual. Incorrect timing can severely affect performance and fuel economy.
* Distributor Points (if equipped): If your 1973 Pontiac 400 still uses points, the dwell angle should be adjusted according to your owner's manual. Typically, it's in the range of 28° to 32°. Point gap is usually around 0.016" to 0.018". Electronic ignition conversions are highly recommended for reliability and improved performance.
* Carburetor: The carburetor needs to be properly adjusted for idle speed, mixture, and throttle response. This is best left to someone experienced in carburetor tuning as it involves adjusting numerous screws and linkages. Vacuum leaks will disrupt the mixture. The specifications will vary depending on the carburetor type (Rochester Quadrajet was common). Your owner's manual should provide specifications or refer you to a carburetor adjustment procedure.
* Air Filter: Replace with a clean air filter element.
* PCV Valve: Inspect and replace if necessary.
* Vacuum Hoses: Inspect for leaks, cracks, or deterioration. Replace as needed.
* Fuel Filter: Replace with a new fuel filter.
Critical Considerations:
* Owner's Manual: This is your primary source for tune-up specs. The information above is a general guideline, not a substitute for the factory recommendations.
* Repair Manual: A Pontiac-specific repair manual (like a Chilton's or Haynes) will provide detailed instructions and specifications for your specific engine code.
* Professional Mechanic: If you're not comfortable performing these tasks yourself, it's best to take your vehicle to a qualified mechanic experienced with classic Pontiacs. Improper tuning can damage your engine.
Don't attempt to guess; accurate specifications are vital for the longevity and performance of your engine. Find your owner's manual or a reputable repair manual for your exact engine code.
