Adjusting the carburetor on your classic Volkswagen can seem daunting, but with a systematic approach, it’s manageable. This guide provides a step-by-step walkthrough for adjusting a 34 PICT 3 carburetor, commonly found on 1974 VW models.
Initial Setup: Volume and Bypass Screws
Begin by turning the volume control screw (the smaller screw on the left side of the carb) clockwise until it gently seats. Avoid excessive force. Back the screw out three full turns. Repeat this process for the larger bypass screw: turn it clockwise until seated, then back it out three full turns. This establishes a baseline setting for further adjustments.
Warming Up and Setting Idle Speed
Start the engine and let it warm up completely, ensuring the choke cam is fully disengaged. With the engine warm, adjust the large bypass screw until the engine idles at approximately 900 RPM, as indicated on your tachometer. This sets the initial idle speed.
Fine-Tuning with the Volume Control Screw
Next, use the small volume control screw to fine-tune the idle speed. Turn the screw clockwise to increase RPM. Continue turning until the RPM begins to decrease. Then, slowly turn the screw counterclockwise, back to the point where the engine achieves its highest RPM. From this peak RPM, back the screw out slightly until the RPM drops by about 30. This optimizes the air-fuel mixture at idle.
Final Bypass Adjustment
Return to the large bypass screw and make minor adjustments, typically counterclockwise, to bring the idle speed back to the target 900 RPM. This final adjustment compensates for the changes made with the volume control screw.
Addressing Potential Fuel Leaks
While adjusting your carburetor, inspect all hoses and the throttle shaft bushing area for fuel leaks. If fuel is leaking from the throttle shaft bushings, consider having the carburetor re-bushed. Since you mentioned experiencing fuel smells, particularly during turns, also check your fuel tank and related fittings for any leaks.
