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Tillotson 43-388 Low Speed/Idle Mixture Screw
43-388 Tillotson Low Speed/Idle Mixture Screw
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Tillotson 43-388 Low Speed/Idle Mixture Screw

Part Number: 43-388
Online Price: $5.99
43-388 OEM Tillotson Low Speed / Idle Mixture Screw for HL Carburetors
Availability: In Stock.

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Description

43-388 Tillotson OEM Low Speed / Idle Mixture Screw – Steel Screw for HL Gas Carburetors


The 43-388 Tillotson Low Speed (Idle) Mixture Screw is a genuine OEM adjustment screw designed for the low side fuel circuit of Tillotson HL carburetors—commonly used on gasoline-powered small engines in both 2-cycle and 4-cycle configurations.


Often referred to as an idle mixture screw, this component does more than just manage idle. It plays a critical role in low-speed, midrange, and transitional throttle response, acting as a key part of the carburetor's main fuel circuit—essential for smooth acceleration and responsive power delivery.


Key Features:

  • OEM Part #43-388 – Guaranteed fit and function for supported HL-series Tillotson carburetors.
  • Precision Low-Side Fuel Control – Adjusts fuel delivery to the low side well for optimal throttle response and idle.
  • Steel Construction – High-quality OEM steel for durability, corrosion resistance, and long-term tuning stability.
  • Not Just Idle – Impacts low-end torque, throttle transition, and midrange performance.
  • Ideal for Gasoline Engines – Optimized for gasoline-fueled engines, especially small-displacement 2-cycle motors.


Tuning Note:

  • On 2-cycle engines, this screw allows proper idle and low-speed tuning.
  • On 4-cycle engines running methanol, carburetors tend to run too rich at idle. In such cases, avoid using this screw to set the idle—improper adjustment can cause hesitation or flat acceleration.


Compatible Tillotson Carburetor Models:

  • HL-1A, HL-129E, HL-132H, HL-166B, HL-166C, HL-189F
  • HL-227A, HL-227E, HL-229A, HL-232A, HL-232E
  • HL-250A, HL-250B, HL-250C, HL-250D, HL-250E
  • HL-274E, HL-292G, HL-299E, HL-304E, HL-304WXG
  • HL-306A, HL-321E, HL-324A, HL-334A, HL-334AA
  • HL-334AB, HL-334B, HL-334WXG, HL-352A, HL-360A, HL-375A

Always confirm your carburetor model before ordering to ensure proper fitment.


Ideal For:

  • Racing go-karts and performance small engines
  • 2-cycle gasoline-powered engines using Tillotson HL carbs
  • Carburetor rebuilds and tuning setups
  • Replacement of worn, stripped, or missing idle mixture screws

FAQ

What is the Tillotson 43-388 Idle Mixture Screw used for?

The 43-388 screw controls fuel delivery to the low-speed circuit of Tillotson HL carburetors. It impacts idle, low-end, and midrange performance, not just idle RPM.


Which Tillotson carburetors are compatible with the 43-388 screw?

It fits over 30 models including: HL-129E, HL-132H, HL-166B/C, HL-189F, HL-227A/E, HL-250A–E, HL-274E, HL-304E/WXG, HL-334A/B/AA/AB, HL-360A, HL-375A, and more.


Can I use this screw on a 4-cycle engine?

Yes, but caution is required. On 4-cycle engines using methanol, the carb runs too rich at idle. Don’t use this screw to set idle in such cases—it can cause hesitation or flat acceleration.


Is the 43-388 screw compatible with gasoline engines?

Yes, this screw is specifically designed for gasoline-powered Tillotson carburetors and works best on 2-cycle small engines.


Is this an OEM Tillotson part?

Absolutely. The 43-388 mixture screw is an OEM steel component, manufactured to match factory specifications for durability and performance.

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