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Tillotson 24B-289 Inlet Tension Spring
24B-289 Tillotson Inlet Tension Spring
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Tillotson 24B-289 Inlet Tension Spring

Part Number: 24B-289
Online Price: $1.09
Tillotson 24B-289 Inlet Tension Spring – Diaphragm Carb Pop-Off
Availability: In Stock.

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Description

Tillotson 24B-289 Inlet Tension Spring – Pop-Off Control for Diaphragm Carburetors


The Tillotson 24B-289 Inlet Tension Spring is a precision OEM component used to control pop-off pressure in diaphragm-style carburetors. This spring plays a key role in fuel delivery by regulating when the inlet needle opens, particularly during low-speed and idle operation.


By maintaining proper spring tension under the fulcrum arm, it ensures clean throttle response, prevents flooding, and supports consistent carburetor performance under varying conditions.


Key Features:

  • OEM Part Number: 24B-289
  • Controls pop-off pressure in diaphragm carburetors
  • Ensures proper fuel metering to high and low side circuits
  • Helps prevent bogging or rich conditions at idle
  • Installs under the fulcrum arm, above the needle valve
  • Compatible with select Tillotson HL, HR, HW, and other series


Understanding Pop-Off Pressure vs. Fuel Pressure:

Pop-off pressure refers to the internal pressure required to lift the needle valve off its seat, allowing fuel into the metering chamber. It is influenced by:

  • Spring tension (like the 24B-289)
  • Fulcrum arm height
  • Needle type and seat condition

Important Note:
Pop-off pressure is not the same as fuel pressure.

  • Most diaphragm fuel pumps deliver under 1 PSI
  • A spring rated for 10 PSI pop-off does not require 10 PSI fuel pressure to operate
  • Instead, it reacts to diaphragm pulses and internal vacuum created by the engine


Tuning Tips:

To fine-tune pop-off pressure:

  • Use springs with different gram ratings (light = opens easier, heavy = opens later)
  • Adjust fulcrum arm height precisely
  • Add shims under the spring for minor pressure changes

Always test with fresh diaphragms and consistent needle/seat assemblies to ensure reliable readings and tuning results.


Ideal For:

  • Rebuilding or tuning Tillotson diaphragm carburetors
  • 2-stroke performance and racing engines
  • Small engine service professionals
  • Improving throttle crispness and fuel delivery accuracy

FAQ

Q1: What is the function of the Tillotson 24B-289 inlet spring?

A: The 24B-289 spring controls pop-off pressure in Tillotson diaphragm carburetors. It determines how easily the inlet needle valve opens to allow fuel into the metering chamber, especially at idle and low throttle.


Q2: Is pop-off pressure the same as fuel pressure?

A: No. Pop-off pressure is an internal carburetor setting, determined by the spring tension and fulcrum arm height. It is not related to external fuel pressure, which rarely exceeds 1 PSI in small engines.


Q3: What happens if my pop-off spring is too weak or too strong?

A:

  • A weak spring may cause flooding or bogging due to early needle opening.
  • A strong spring may delay fuel delivery, causing hesitation or lean conditions.
    Tuning involves balancing spring tension with your engine’s needs.


Q4: Can I tune pop-off pressure without replacing the spring?

A: Yes, to a degree. You can:

  • Adjust the fulcrum arm height
  • Add or remove shims under the spring
    But for precise tuning, using a properly rated spring like the 24B-289 is essential.


Q5: What carburetors is the 24B-289 spring compatible with?

A: It’s primarily used in Tillotson diaphragm carburetors (such as HL, HR, HW series). Always confirm your carburetor model or refer to our reference guide to ensure proper fit.

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