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EC 420INT EC Intake Manifold 1.125 HL to GX390/420
420INT EC Intake Manifold 1.125" HL to GX390/420
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EC 420INT EC Intake Manifold 1.125 HL to GX390/420

Part Number: 420INT
Online Price: $41.99
EC 420INT Intake Manifold – Adapt HL 1.125” Carb to GX390/420 Clone Engines
Availability: In Stock.

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Description

EC 420INT Billet Intake Manifold – 1.125” HL Tillotson to GX390/420 Clone Engines


Unlock Big Block Power with Precision Carburetor Adaptation


The EC 420INT Intake Manifold is purpose-built to adapt 1.125” bore Tillotson HL-series carburetors—such as the HL-380 or X380 Intimidator—to Honda GX390, GX420, and comparable big block clone engines including Predator 420, 440, 460, and 459cc models.

Designed for kart racers and engine builders seeking superior airflow and carburetor tuning adjustability, this billet manifold delivers a significant performance advantage over stock GX390/420 carb setups—especially in spec-class 420cc kart racing.


Key Features:

  • Fits 1.125” Tillotson HL-style carburetors (e.g., HL-380, EC X380)
  • Adapts to GX390, GX420, 440, 460 Honda/Clone/Predator engines
  • Improves airflow and tuning capability over stock carburetors
  • Precisely machined to match intake port geometry for smooth, laminar flow
  • Integrated pulse port for consistent diaphragm carb operation at high RPM
  • All mounting hardware included


Recommended Setup:

While this manifold supports any 1.125” HL carb, EC highly recommends the X380-7 Intimidator for best results. It features a 3-piece throttle shaft and proprietary fuel circuit design, optimized specifically for OHV big block engines—not flatheads like the original HL-380.


Engineered for Performance & Flow Efficiency

This CNC-machined manifold is designed to align seamlessly with the intake port on GX390/420 heads (note: port shape may vary by brand/model). This precise match eliminates turbulence, promoting efficient air/fuel delivery and improving throttle response.


By pairing a diaphragm-style Tillotson carb with this manifold, you benefit from a superior intake angle and better high-RPM pulse action, giving your engine the responsiveness it needs for competitive racing.


A Note on Intake Length & Pulse Signal:

Tuning intake length for performance gains is complex. A longer runner may improve low-end torque—but on a diaphragm carb, it can weaken the pulse signal, hurting performance. The 420INT is optimized for the proper balance of length, angle, and flow for Tillotson-style carbs. Unless you're doing scientific testing with proper equipment, altering intake length may produce marginal or unpredictable gains.


Compatibility:

  • Carburetors: Tillotson HL-380, EC X380 Intimidator, or any 1.125” HL-style carb
  • Engines:
    • Honda GX390 / GX420
    • Predator 420 / 440 / 460
    • 459cc Harbor Freight (non-hemi and hemi versions)
    • Most GX-style big block clones


Included:

  • 1x EC 420INT Billet Intake Manifold
  • Mounting hardware
  • Pre-drilled pulse port
  • Smooth-bore intake path, no gaskets required for port sealing (if using matched carb)

FAQ

1. Which carburetors fit this intake manifold?

It fits 1.125” bore Tillotson HL carburetors, including the HL-380 and EC X380 Intimidator.


2. What engines are compatible with the 420INT?

It adapts HL carburetors to GX390, GX420, and clones such as Predator 420/440/460, Ducar 420, and other GX-style big block engines.


3. Does it include a pulse port?

Yes, the intake includes a precisely located pulse port to ensure reliable diaphragm carb operation at high RPM.


4. Is this intake designed for methanol or gasoline?

The intake itself is neutral. However, it’s commonly used in methanol race builds, especially when paired with EC’s X380-7 carburetor, which is tuned specifically for 420cc class methanol racing.


5. Can I use a different HL carb like the HL-360 or 334?

No, they can fit physically bolt on—but the pulse hole will not line up. We have our 419INT which is made for 1-inch Tillotson HL carburetors

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