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021 Inlet Tension Pop Off Spring
021 Inlet Tension / Pop-Off Spring
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021 Inlet Tension Pop Off Spring

Part Number: 021
Online Price: $2.00
021 Inlet Tension Pop-Off Spring – Fuel Control for Diaphragm Carburetors
Availability: In Stock.

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Description

021 Inlet Tension Pop-Off Spring – For Diaphragm Carburetor Tuning


The 021 Inlet Tension Pop-Off Spring is a precision component used to control pop-off pressure in diaphragm-style carburetors. This pressure directly affects how fuel flows into the high- and low-speed circuits, particularly at idle and low RPM operation.


Pop-off pressure is often misunderstood. It is not the same as fuel pressure and does not control or reflect what your fuel pump produces. Most fuel pumps used with diaphragm carburetors generate approximately 1 PSI, while pop-off pressure can range from 5–15 PSI depending on spring tension and installation height.

For example, a 10 PSI pop-off reading does not mean your fuel system must produce 10 PSI to open the needle valve. Instead, it refers to the internal pressure needed to lift the inlet needle, allowing fuel to enter the metering chamber.


Product Details:

  • Part Number: 021
  • Designed for Tillotson-style diaphragm carburetors
  • Helps fine-tune low-speed fuel delivery and throttle response
  • Works with most HL, HR, and similar carburetor models
  • Pop-off pressure is determined by spring tension and install height


Use Case:

Perfect for 2-stroke small engines, kart racing setups, or chainsaws where precise fuel control and reliable tuning are critical. The 021 spring allows for consistent fuel metering performance, especially in environments where throttle sensitivity matters.

FAQ

Q1: What does the 021 Inlet Tension Spring do in a carburetor?
A: It regulates pop-off pressure, which controls when the inlet needle opens to let fuel into the carburetor’s metering cavity. This affects low-speed fuel delivery and overall throttle response.


Q2: Is pop-off pressure the same as fuel pressure?
A: No. Pop-off pressure is internal carburetor pressure needed to lift the needle valve. Fuel pumps typically provide only 1 PSI, while pop-off pressure is determined by spring tension, not pump output.


Q3: What carburetors are compatible with the 021 pop-off spring?
A: It fits most Tillotson-style diaphragm carburetors, including HL and HR models, commonly used in 2-stroke racing engines, karting, chainsaws, and small engines.


Q4: Can I adjust pop-off pressure without changing the spring?
A: Minor adjustments can be made by shimming or altering spring install height, but for major tuning changes, switching to a different-rated spring like the 017, 021, or 024 is recommended.


Q5: How do I measure or test pop-off pressure?
A: Use a pop-off pressure gauge specifically designed for diaphragm carburetors. Always test in a clean environment and refer to your carb or engine manufacturer’s spec for proper tuning.

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