3.5mm Auxillary Venturi For EPC

OVERVIEW

Precision fuel delivery is the backbone of any high-performance air-cooled engine, and the EMPI 3.5mm Auxiliary Venturi for EPC carburetors is a critical component in achieving that perfect stoichiometric balance. Often referred to as a ''booster venturi,'' this part sits suspended within the main venturi to create a localized low-pressure zone that pulls fuel from the emulsion tube circuit. By utilizing a 3.5mm profile, this auxiliary venturi ensures a crisp vacuum signal even at lower RPMs, allowing for a seamless transition from the idle circuit to the main jets. Without a high-quality, perfectly seated auxiliary venturi, your engine may experience the dreaded ''flat spot'' during acceleration, leading to sluggish performance and uneven power delivery across the power band. Whether you are building a daily-driven 1600cc upright or a fire-breathing 2332cc stroker, the consistency of your fuel atomization starts right here.

The EMPI EPC series carburetors have become a staple in the VW community for their reliability and tuneability, but they are only as good as the internal components used to calibrate them. This 3.5mm auxiliary venturi is engineered to exacting tolerances to ensure that air velocity is maximized without causing unnecessary turbulence. When upgrading or rebuilding your dual-carburetor setup, it is essential to inspect these components for wear, casting imperfections, or loose fitment within the carb body. A loose auxiliary venturi can vibrate, leading to inconsistent fuel draw and making it nearly impossible to sync your carburetors properly. By choosing this genuine EMPI replacement part, you are ensuring that your EPC, HPMX, or Weber IDF-style carburetors maintain the high-velocity airflow required to keep your flat-four running cool, efficient, and powerful. Don''t let a worn-out or mismatched venturi stand between you and the smooth throttle response your Volkswagen deserves.

FITMENT

• EMPI EPC Carburetors: 40mm, 44mm, and 48mm models.
• Weber IDF Carburetors: Compatible with most 40, 44, and 48 IDF series.
• HPMX Carburetors: Direct fit for HPMX dual-carburetor kits.
• Volkswagen Beetle: All years equipped with dual EPC/IDF style carburetors.
• Volkswagen Karmann Ghia: Type 1 based performance engines.
• Volkswagen Bus/Transporter: Type 2 (Bay Window and Split Window) with performance dual carbs.
• Volkswagen Type 3: Notchback, Squareback, and Fastback performance builds.
• VW-Based Sand Rails & Buggies: Off-road applications requiring precise fuel metering.

SPECS

• Product Type: Auxiliary Venturi (Booster Venturi).
• Size: 3.5mm.
• Manufacturer Part Number: 43-5687-0.
• GTIN: 707924236323.
• Material: High-grade die-cast zinc alloy for thermal stability.
• Weight: 0.1 lbs.
• Application: Main circuit fuel atomization.
• Compatibility: Designed for EMPI Performance Carburetors (EPC).

PRO TIPS

1. Ensure Perfect Alignment and Seating

When installing the auxiliary venturi, it is absolutely vital that the discharge arm aligns perfectly with the fuel outlet in the carburetor body. If the venturi is slightly rotated or not seated fully, it will disrupt the vacuum signal and cause a lean condition on that specific cylinder. I always recommend a light press with your thumb to ensure it is bottomed out; you should feel a distinct ''seat.'' If it feels loose or wobbles, it can lead to harmonic vibrations at high RPM, which will froth the fuel and cause an unpredictable air-fuel ratio. Double-check that the retention spring or clip is applying even pressure to keep the venturi locked in place during high-vibration off-road or track use.

2. Inspect for Casting Flash and Burrs

Even with high-quality EMPI components, a master tuner knows to inspect every internal part for tiny casting imperfections. Use a magnifying glass to check the internal bore of the 3.5mm auxiliary venturi for any microscopic burrs or ''flash'' left over from the manufacturing process. These tiny obstructions can cause air turbulence, which negatively impacts fuel atomization. If you find any, use a piece of 1000-grit sandpaper or a fine needle file to gently smooth the edges. A mirror-smooth finish on the venturi surfaces ensures the highest possible air velocity, which translates directly to a more responsive engine and better fuel economy during cruising speeds.

3. Sync Your Signal Across All Barrels

If you are running a dual-carburetor setup, consistency is your best friend. Always ensure that you are using the same size auxiliary venturi (in this case, 3.5mm) across all four barrels. Mixing sizes or using one old, pitted venturi with three new ones will create a pressure differential that makes synchronizing the carbs a nightmare. When using a Uni-Syn or a snail-style flow meter, the auxiliary venturi plays a major role in the signal the meter receives. If you find that one barrel is consistently ''lazy'' compared to the others despite identical jetting, swap the auxiliary venturis between barrels to see if the problem follows the part. This is a pro-level diagnostic trick to identify a venturi that may have internal casting flaws or a restricted fuel passage.