36mm Venturi, for 40-44 HPMX & 44 IDF Weber Carburetors

OVERVIEW

Precision airflow management is the heartbeat of any high-performance air-cooled engine, and the 36mm Venturi for 40-44 HPMX and 44 IDF Weber Carburetors is the definitive tool for fine-tuning your induction system. When you are looking to squeeze every ounce of horsepower out of your dual-carb setup, the venturi (or main choke) is what determines the velocity of the air passing through the carburetor throat. By selecting a 36mm bore, you are optimizing your engine for a robust mid-range and top-end pull, providing the necessary vacuum signal to pull fuel efficiently through the main circuit while maintaining enough volume for high-RPM demands. Whether you are building a spirited 1776cc street engine or a high-revving 2110cc weekend warrior, these precision-cast venturis ensure that your air-fuel mixture is consistent, atomized, and ready for combustion.

At Appletree Auto, we know that "one size fits all" never applies to custom VW builds. Swapping to a 36mm venturi allows you to tailor your Weber or HPMX carburetors to your specific camshaft profile and cylinder head flow characteristics. If your current setup feels sluggish or "runs out of breath" at higher speeds, moving to a larger 36mm choke can unlock the restricted airflow that is holding your Type 1, Type 2, or Type 3 back. These are genuine EMPI components, engineered to fit perfectly within the carburetor body without the need for machining or complex modifications. By upgrading your venturis, you are not just changing a part; you are re-calibrating the entire power band of your Volkswagen, ensuring that the transition from the idle circuit to the main jets is seamless and responsive under heavy throttle.

FITMENT

• Carburetor Compatibility: Weber 44 IDF, EMPI 44 HPMX, and EMPI 40 HPMX Series.
• Volkswagen Type 1: Beetle, Super Beetle, and Karmann Ghia (1954-1979).
• Volkswagen Type 2: Bus, Transporter, and Kombi (1955-1971).
• Volkswagen Type 3: Squareback, Fastback, and Notchback (1961-1973).
• Volkswagen Type 181: The Thing (1973-1974).
• Custom Builds: Fits all sand rails, buggies, and kit cars utilizing dual 40/44 IDF style intake manifolds.

SPECS

• Internal Diameter: 36mm Precision Bore.
• Material: High-quality die-cast zinc alloy for thermal stability.
• Finish: Machined smooth for laminar airflow and reduced turbulence.
• Manufacturer Part Number: 43-5611-0.
• Quantity: Sold individually (two required per carburetor, four required for a dual-carb engine).
• Application: Main Venturi / Choke for IDF/HPMX series carburetors.

PRO TIPS

1. Calculate Your Optimal Sizing

Selecting the right venturi is a balancing act between low-end torque and high-end horsepower. As a general rule for air-cooled VWs, a 36mm venturi is ideal for engines ranging from 1835cc to 2110cc that spend a lot of time in the mid-to-high RPM range. If you find that your engine has a "stumble" or "flat spot" during acceleration that can''t be tuned out with jets, your venturis might be too large for your displacement, causing a weak vacuum signal. Conversely, if your 44 IDFs feel restricted at 5,000 RPM, the 36mm upgrade is the perfect solution to let that engine breathe.

2. Sync Your Jetting with Your Venturi

Always remember that changing your venturi size fundamentally changes the physics of how your carburetor pulls fuel. When you increase the venturi size to 36mm, the air velocity at lower RPMs decreases, which usually requires a larger main jet to compensate for the reduced vacuum signal. Don''t make the mistake of swapping venturis without having a selection of main jets and air correctors on hand. We recommend starting with a main jet that is roughly 4 to 4.3 times the size of your venturi (e.g., a 145 or 150 main jet with a 36mm venturi) as a baseline for tuning.

3. Inspect for Proper Seating

During installation, it is critical to ensure the venturi is fully seated and locked in place by the carburetor''s set screw. Even a tiny amount of movement or an air leak around the perimeter of the venturi can cause erratic idling and impossible-to-tune lean conditions. Before sliding the new 36mm venturi into the throat, clean the carburetor body thoroughly with carb cleaner to remove any old fuel varnish or debris. Once installed, apply a small drop of blue threadlocker to the retaining screw to ensure vibrations from your high-performance engine don''t let the venturi vibrate loose over time.