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Tillotson HL Idle Speed Screw
15C-9 Tillotson HL Idle Speed Screw
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Tillotson HL Idle Speed Screw

Part Number: 15C-9
Online Price: $2.69
15C-9 Tillotson Idle Speed Screw – Genuine OEM for HL-Series Carburetors
Availability: In Stock.

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Description

15C-9 Tillotson Idle Speed Screw – OEM Fit for HL Series Carburetors


OEM Adjustment Screw | Idle Position Control | Racing-Ready Setup

The Tillotson 15C-9 Idle Speed Screw is a precision-machined OEM replacement screw that adjusts the idle position of the throttle butterfly in HL-series Tillotson carburetors. By controlling how far the throttle shutter remains open at idle, it directly influences the engine’s idle speed (RPM).

This screw is critical for setting up your carburetor's baseline throttle position, whether you're tuning for smooth idle or using it as a throttle stop in racing engines.


Use in 4-Cycle Racing Applications

In 4-cycle racing, we do not recommend setting a traditional idle with this screw, as idling can cause the engine to run excessively rich and negatively affect off-the-line acceleration.

Instead, use the idle speed screw as a mechanical stop to:

  • Prevent the throttle butterfly from closing too far
  • Avoid wear or damage to the carburetor body and throttle assembly

Want to learn more about idling in racing setups? Check out our blog on 4-cycle carburetor tuning.


Key Features:

  • Genuine Tillotson OEM Part – Reliable fit and finish
  • Precise Throttle Control – Adjusts idle or sets throttle stop
  • Essential for Rebuilds & Tuning – Works with most HL carburetors
  • Durable Steel Construction – Built for long service life


Compatible With:

The 15C-9 Idle Speed Screw fits most Tillotson HL-series carburetors, including:

HL Models: HL-1A, HL-129E, HL-132H, HL-166B/C, HL-189F, HL-227A/E, HL-229A, HL-232A/E, HL-250A-E, HL-274E, HL-292G, HL-293A/F, HL-299E, HL-304E/WX/WXA/WXG, HL-306A, HL-314E/F/G, HL-324A, HL-334A/AA/AB/B, HL-339A, HL-341A, HL-342A, HL-348A-E, HL-352A, HL-355A-E, HL-357A/B, HL-360A-C, HL-365A/B, HL-366A, HL-368A, HL-371A, HL-374A, HL-380A/B, HL-383A, HL-384A/B, HL-385A, HL-388A, HL-395A
And many more HL-series models.

May not compatible with non-HL Tillotson carburetors or HD-series models.


Pro Tip:

If you're running a racing kart or performance engine, use this screw to stop the throttle blade just shy of full closure to protect the throttle plate and carb body from wear—not for idle tuning.


Why Choose the 15C-9 Idle Speed Screw?

  • ?? OEM-quality fit and finish
  • ?? Critical for safe throttle setup
  • ?? Compatible with a wide range of HL carburetors
  • ?? Designed for both standard and high-performance use

FAQ

Q1: What does the Tillotson 15C-9 idle speed screw do?
A: It adjusts the throttle shutter (butterfly) position at idle, setting the engine's idle RPM or acting as a throttle stop in racing applications.


Q2: Is this screw used for idle tuning in 4-cycle racing?
A: No. In 4-cycle racing setups, it's not used to set idle RPM. Instead, it acts as a stop screw to prevent the throttle shutter from closing too far and damaging the carb body.


Q3: Which Tillotson carburetors are compatible with the 15C-9 screw?
A: It fits most HL-series models, including HL-1A, HL-129E, HL-250C, HL-304WX, HL-360B, and many more. See the full compatibility list in the product description.


Q4: Can this screw be used on non-HL Tillotson carburetors?
A: No, the 15C-9 is specifically designed for Tillotson HL-series carburetors and may not fit other series like HD or HW.


Q5: Do I need to adjust this screw during a rebuild?
A: Yes. When rebuilding or reinstalling your carburetor, use the 15C-9 screw to reset the throttle plate position for proper airflow and protection.


Q6: What’s the screw made of?
A: The 15C-9 idle speed screw is made from high-strength, corrosion-resistant steel to ensure long-lasting durability and reliable performance.

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