42mm Venturi, for 48-55 Dco Weber Carburetors

OVERVIEW

Precision tuning is the difference between a sluggish engine and a high-performance machine that screams down the track. When you are running large-bore Weber DCO side-draft carburetors, the venturi (or main choke) is the most critical component for determining the airflow characteristics and power band of your air-cooled powerplant. This EMPI 42mm Venturi is engineered specifically for the 48, 50, and 55 DCO series, providing the necessary restriction to create a strong vacuum signal at the auxiliary venturi. By narrowing the carb throat to 42mm, you accelerate the incoming air, ensuring that fuel is atomized efficiently even at high RPMs. For racers and high-output street enthusiasts, this component is the key to unlocking the volumetric efficiency required for maximum horsepower gains in large-displacement Type 1 or Type 4 engines.

Choosing the right venturi size is a delicate balancing act that Appletree Auto understands perfectly. While a smaller venturi increases bottom-end torque and throttle response, a 42mm bore is designed for those who need massive top-end flow without hitting a wall. These venturis are manufactured with exacting tolerances to ensure a perfect fit within the carburetor body, preventing air leaks that could lead to lean conditions and potential engine damage. Whether you are building a weekend drag racer or a high-compression street terror, these EMPI units offer the reliability and performance consistency that Weber carburetors are famous for. Don''t let a mismatched intake signal hold back your build; upgrade to the correct venturi size to ensure your fuel delivery matches your engine''s true potential.

FITMENT

This 42mm Venturi is designed for high-performance side-draft carburetor applications. Please verify your carburetor body size before ordering, as these are specific to the DCO series.

• Weber Carburetor Models: Fits Weber 48 DCO, 50 DCO, and 55 DCO Side-Draft Carburetors.
• Volkswagen Type 1: Custom Beetle, Karmann Ghia, and Thing models equipped with DCO side-draft manifolds.
• Volkswagen Type 2: Bus, Transporter, and Westfalia models running high-performance side-draft setups.
• Volkswagen Type 3: Squareback, Notchback, and Fastback performance builds.
• Volkswagen Type 4: 1700cc, 1800cc, and 2000cc engines utilized in Porsche 914 or VW Bus conversions with DCO carbs.
• Custom Sand Rails & Buggies: Ideal for high-displacement off-road engines requiring maximum airflow.

SPECS

Detailed technical specifications for the EMPI 43-5620-0 Venturi:

• Internal Diameter: 42mm (Bore Size).
• Compatibility: Weber 48 / 50 / 55 DCO Series.
• Material: High-grade precision-machined alloy for thermal stability.
• Finish: Smooth internal taper for laminar airflow and reduced turbulence.
• Part Number: 43-5620-0.
• Quantity: Sold individually (Each).
• Function: Controls the "Venturi Effect" to draw fuel from the main circuit.

PRO TIPS

Tip 1: Matching Venturi Size to Engine Displacement

When selecting a venturi, remember that the 42mm size is generally reserved for large-displacement engines (typically 2100cc and above) or high-revving race engines. If your venturi is too large for your engine''s displacement, you will experience a "bog" or hesitation at low RPMs because the air velocity isn''t high enough to pull fuel through the main jets. Always consult a CFM chart or talk to our specialists at Appletree Auto to ensure a 42mm bore matches your cam profile and head flow, as this is a high-flow component meant for the upper registers of the power band.

Tip 2: Re-Jetting is Mandatory

It is a common mistake to swap venturis without adjusting the rest of the carburetor''s calibration. When you increase the venturi size to 42mm, you are fundamentally changing the pressure differential inside the carburetor. This almost always requires a change in your Main Jets and Air Correctors. Generally, a larger venturi requires a larger main jet to maintain the correct air-fuel ratio. We recommend starting slightly rich and tuning down to avoid the "lean pop" that can occur when the increased airflow outpaces the fuel delivery of your old jetting setup.

Tip 3: Inspection and Seating

Before installing your new 42mm venturis, take a moment to inspect the internal bores of your Weber DCO bodies for any debris or old fuel varnish. The venturi must seat perfectly flush against the carburetor wall to prevent "false air" from entering the stream. If the venturi is loose or misaligned, it can cause erratic idling and inconsistent synchronization between your carburetors. Use a small amount of carb cleaner to ensure the mating surfaces are spotless, and always double-check that the set screws are tightened properly to lock the venturi in place during high-vibration racing conditions.