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Tillotson 24B-323 Inlet Tension Spring
24B-323 Tillotson Inlet Tension Spring
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Tillotson 24B-323 Inlet Tension Spring

Part Number: 24B-323
Online Price: $1.59
Tillotson 24B-323 OEM Inlet Tension Spring – 26g Pop-Off Pressure
Availability: In Stock.

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Description

Tillotson 24B-323 Inlet Tension Spring – 26g Pop-Off Control


The Tillotson 24B-323 Inlet Tension Spring (commonly known as a pop-off spring) plays a critical role in regulating fuel flow within diaphragm-style carburetors. Installed beneath the fulcrum arm, this spring directly influences pop-off pressure, which determines how and when the needle valve opens—particularly at low RPM and throttle transitions.


This spring is a genuine OEM Tillotson part, engineered for consistent performance, accurate tuning, and long-term durability in demanding 2-stroke applications.


Key Features:

  • OEM Part Number: 24B-323
  • Spring Weight Rating: 26 grams
  • Function: Controls pop-off pressure in diaphragm carburetors
  • Position: Installs between the fulcrum arm and carburetor body
  • Material: Precision-wound, corrosion-resistant spring steel
  • Application: Ideal for fine-tuning fuel delivery, especially on race engines


Fits the Following Tillotson Carburetor Series:

  • HW Series
  • HB Series
  • HC Series
  • HL Series
  • HR Series
  • HM Series
  • HX Series


Tuning Tip:

Pop-off pressure is not the same as fuel pressure. It refers to the pressure needed to lift the needle valve off its seat—governed by the tension of this spring and the fulcrum arm height.

Your fuel pump may only produce ~1 PSI, while pop-off pressure can be 10 PSI or higher depending on the spring. The carburetor does not require the fuel pump to exceed the spring rating to function. Instead, the diaphragm’s pulsing action, influenced by spring tension, regulates when and how much fuel enters the metering chamber.


For Best Results:

  • Use fresh metering diaphragms during tuning
  • Adjust fulcrum arm height for precision control
  • Add shims under the spring for fine pressure changes
  • Swap springs of different weights (gram ratings) to target desired response


Ideal For:

  • 2-stroke race engines
  • Karting, chainsaws, handheld equipment
  • Tuners aiming for optimal throttle response
  • Anyone rebuilding or tuning Tillotson diaphragm carburetors

FAQ

Q1: What does the Tillotson 24B-323 inlet tension spring do?

A: The 24B-323 spring controls pop-off pressure in diaphragm carburetors by determining when the needle valve opens. It helps regulate fuel delivery at low RPMs and is critical for clean, responsive throttle performance.


Q2: What does 26 grams mean in this context?

A: The 26g rating refers to the spring's tension or resistance. Heavier springs (higher gram values) require more pressure to lift the needle, while lighter springs (lower grams) open more easily. Tuning this tension affects low-speed fuel delivery and throttle feel.


Q3: Is this the same as fuel pressure?

A: No. Pop-off pressure is not the same as fuel pressure. Fuel pressure (from the pump) is typically under 1 PSI. Pop-off pressure reflects the resistance of the inlet needle, spring, and fulcrum arm combination.


Q4: Can I change pop-off pressure without changing the spring?

A: Yes. You can fine-tune pop-off pressure by:

  • Adjusting the fulcrum arm height
  • Adding shims under the spring
    However, for more significant changes, swapping to a different spring weight is recommended.


Q5: Which carburetors does the 24B-323 spring fit?

A: It fits most Tillotson diaphragm-style carburetors, including the HW, HL, HB, HR, HM, HC, and HX series. Always verify your carb model before ordering.


Q6: Should I install this during a rebuild?

A: Absolutely. If you're rebuilding your carb or fine-tuning throttle response, replacing the inlet spring ensures consistent fuel metering. It’s especially important when pop-off behavior is inconsistent or when switching fuels (e.g., race gas, ethanol blends).

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