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Tillotson HR High Speed Mixture Screw
43-987 Tillotson HR High Speed Mixture Screw
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Tillotson HR High Speed Mixture Screw

Part Number: 43-987
Online Price: $9.99
43-987 Tillotson HR High-Speed Mixture Screw – OEM Brass Needle
Availability: In Stock.

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Description

43-987 Tillotson HR High-Speed Mixture Screw – OEM Brass Needle for Peak RPM Tuning


The 43-987 Tillotson High-Speed Mixture Screw is an OEM brass adjustment needle used in the high-side fuel circuit of Tillotson HR-series carburetors. Designed for precision fuel metering at wide-open throttle, this screw plays a critical role in optimizing top-end power and throttle response in racing engines.


The high-speed screw regulates fuel flow to the high-side nozzle or orifice and should be tuned at peak RPM, typically on the longest straightaway of the track. Ideal for 2-cycle and methanol-fueled 4-cycle racing engines, it allows fine adjustment of your carburetor’s main fuel delivery under full load.


Key Features:

  • OEM Tillotson high-speed mixture screw
  • Precision-machined from durable brass
  • Controls fuel flow to the high-speed circuit (main jet area)
  • Crucial for tuning peak RPM and wide-open throttle performance
  • Designed for racing use on Tillotson HR and select HL models


Tuning Tip:

Adjust the high-speed screw only at full throttle during racing conditions. Avoid setting it based on idle or low-RPM behavior—this screw governs the main fuel circuit at maximum engine load.


Specifications:

  • Material: Brass
  • Function: High-speed fuel metering
  • OEM Part Number: 43-987


Fits the Following Tillotson Carburetors:

  • HR Series:
    HR-181B
    HR-184A
    HR-190A
    HR-191C
    HR-191G
    HR-196A
  • Also Fits: HL-375A

Always check your carburetor model before ordering. This screw is designed for use with HR high-side circuits and is not interchangeable with low-side adjustment screws.

FAQ

What is the 43-987 Tillotson mixture screw used for?

It controls fuel delivery to the high-speed (main) circuit of Tillotson HR carburetors. This is the circuit tuned for peak RPM and wide-open throttle.


Which carburetors are compatible with the 43-987 screw?

This OEM brass mixture screw fits the following models:

  • HR-181B
  • HR-184A
  • HR-190A
  • HR-191C
  • HR-191G
  • HR-196A
  • HL-375A


Is the 43-987 screw compatible with methanol?

Yes. It is commonly used on methanol-fueled open carburetors for racing and is ideal for applications requiring precise fuel control at full throttle.


When should I adjust the high-speed screw?

Tune the high-speed needle at full throttle, usually on the longest straight of the track. This ensures optimal fuel delivery when the engine is under the highest load.


Is this screw made of brass?

Yes. The 43-987 is made from precision-machined brass for durability, corrosion resistance, and smooth adjustment.

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