34mm Venturi, for 40-44 HPMX & 44 IDF Weber Carburetors

OVERVIEW

Precision tuning is the secret to unlocking the true potential of your air-cooled engine, and nothing dictates the power band of your Weber or HPMX carburetors quite like the main venturi. These 34mm venturis are engineered to provide the perfect balance between low-end throttle response and high-RPM airflow. When you are building a street-performance 1776cc or a torquey 1914cc engine, the venturi acts as the heartbeat of your fuel delivery system. It creates the pressure differential necessary to pull fuel from the main circuit, and at 34mm, you are looking at a sweet spot that eliminates the "bog" often found with oversized venturis while still allowing the engine to breathe freely at the top of the gear. At Appletree Auto, we know that off-the-shelf carburetors are rarely optimized for every specific displacement; swapping to these 34mm units allows you to tailor your intake velocity to match your cam profile and head flow perfectly.

Quality manufacturing is paramount when it comes to internal carburetor components, as even a minor casting flaw can cause turbulent airflow and inconsistent cylinder filling. These EMPI-manufactured venturis are held to exacting tolerances to ensure a snug fit within the carburetor throat, preventing vacuum leaks and ensuring that every cubic foot of air is directed exactly where it needs to go. Whether you are replacing a damaged original Weber component or upgrading your EMPI HPMX series for a new engine configuration, these 34mm venturis offer the reliability and performance consistency that VW enthusiasts demand. Don''t settle for a "one size fits all" approach to your fuel system; take control of your engine''s volumetric efficiency and feel the difference in crispness and acceleration that only a properly sized venturi can provide.

FITMENT

This 34mm venturi is designed specifically for the following carburetor models and is commonly used on air-cooled Volkswagen applications:

• Weber 44 IDF: Direct replacement or tuning upgrade.
• EMPI 40 HPMX: High-performance tuning option for larger displacement builds.
• EMPI 44 HPMX: Standard or tuning replacement for dual carb kits.
• VW Type 1 Beetle/Bug: All years equipped with dual IDF/HPMX kits.
• VW Type 2 Bus/Transporter: 1600cc to 2000cc upright or pancake engines.
• VW Type 3 Fastback/Squareback: Performance dual-carburetor setups.
• VW Karmann Ghia: All years using performance Weber-style intakes.
• VW Thing (Type 181): Off-road and street performance configurations.
• Custom Sand Rails & Dune Buggies: Ideal for 1835cc, 1914cc, and 2110cc engine builds.

SPECS

• Venturi Size: 34mm Internal Diameter.
• Carburetor Series: Compatible with Weber IDF and EMPI HPMX.
• Material: Precision-cast zinc alloy for thermal stability and smooth airflow.
• Finish: Machined mating surfaces for a leak-free seal.
• Component Type: Main Venturi (removable).
• Quantity: Sold individually (Note: Most dual-carb setups require four total).
• Part Number: 43-5610-0.

PRO TIPS

1. The 4mm Sizing Rule for Street Performance

When selecting your venturi size, a proven rule of thumb for street-driven air-cooled VWs is to choose a venturi that is approximately 4mm smaller than your throttle plate size. For a 40mm HPMX, a 34mm venturi provides an aggressive boost in air velocity which translates to incredible "off-the-line" torque. If you are running 44mm carburetors on a street 1914cc engine, these 34mm venturis will offer a much smoother driving experience in traffic than 36mm units, without sacrificing significant top-end horsepower. Always remember that air velocity creates the "signal" that pulls fuel; if the venturi is too large, the signal is weak, and the car will stumble at low RPMs.

2. Ensure Proper Seating and Lock Screw Alignment

During installation, it is critical that the venturi is fully seated against the shoulder inside the carburetor body. If the venturi is loose, it can vibrate during operation, which leads to "shucking" or wearing out the carburetor throat, eventually causing permanent damage. When tightening the venturi set screw (located on the side of the carb body), ensure the pointed end of the screw aligns perfectly with the dimple or slot on the venturi. We recommend using a small drop of blue thread locker on the jam nut of the set screw to ensure it doesn''t back out due to engine vibration, which is common in high-performance flat-four engines.

3. Re-Jetting is Mandatory After Venturi Changes

You must remember that changing the venturi size completely alters the vacuum signal reaching the main jet circuit. If you are stepping up from a 32mm venturi to this 34mm unit, your engine will now be drawing in more air, which usually requires a larger main jet to maintain the correct air-to-fuel ratio. A common starting point is to multiply the venturi size by 4 to find your main jet (34 x 4 = 136, so start with a 135 or 140 main jet). Always perform a spark plug reading or use a wideband O2 sensor after swapping venturis to ensure you aren''t running lean at wide-open throttle, which can lead to overheating and engine damage.