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Tillotson HR Nozzle Check Valve
363-508 Tillotson Nozzle Check Valve
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Tillotson HR Nozzle Check Valve

Part Number: 363-508
Online Price: $9.99
Tillotson 363-508 Threaded Nozzle Check Valve for HR-Series Carburetors
Availability: In Stock.

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Description

363-508 Tillotson OEM Threaded Nozzle Check Valve – For HR-Series Carburetors


The 363-508 Tillotson Nozzle Check Valve is a threaded OEM safety component designed to prevent damage inside your Tillotson HR carburetor in the event of a backfire. It features a built-in check ball that seals the fuel passage and protects the internal circuits from reverse pressure.


While the length and shape of the nozzle can subtly influence signal and fuel delivery characteristics, the check ball is not a tuning component. Its sole purpose is to act as a safeguard, not a performance modifier.


Key Features:

  • OEM Part #: 363-508
  • Threaded Design – Specifically made for most Tillotson HR-series carburetors
  • Check Ball Function – Seals off the fuel passage during a backfire, preventing internal damage
  • High-Quality Brass Construction – Durable and resistant to corrosion
  • Exact Fit Dimensions:
    • Length: 0.310 inches


Important Installation Notes:

  • The 363-508 is a threaded nozzle, unlike the press-in versions used in some HL carbs. Do not attempt to press-fitthis nozzle into a non-threaded carb.
  • Always remove the high-speed adjustment screw before installing or removing the nozzle to avoid damaging the needle.
  • Be sure to align the side hole of the nozzle with the pick-off hole (the fuel circuit hole where the adjustment screw connects). Misalignment may cause poor performance or tuning issues.
  • If you’re experiencing fuel leaking from the high side at idle, the cause is usually a worn needle valve or leaking seat, not the check valve.


Compatible Tillotson Carburetor Models:

  • HR-181
  • HR-184
  • HR-190A
  • HR-191C
  • HR-191G
  • HR-192A

Always confirm your carburetor model or measure your existing nozzle to ensure proper fit before ordering.


Ideal For:

  • 2-cycle engine builders using Tillotson HR carbs
  • Racing applications requiring OEM-quality parts
  • Small engine repair shops and tuners
  • Replacing damaged or missing threaded nozzle check valves

FAQ

Q1: What is the function of the Tillotson 363-508 nozzle check valve?

A: The 363-508 check valve protects the carburetor from internal damage during a backfire. It uses a check ball to seal the fuel passage and prevent reverse pressure.


Q2: Is this valve a tuning component?

A: No. While the shape and length of the nozzle may influence fuel signal slightly, the check ball itself is strictly for safety and not used for tuning.


Q3: How do I know if this check valve fits my Tillotson carburetor?

A: It fits most Tillotson HR-series carburetors such as HR-181, HR-184, HR-190A, HR-191C, HR-191G, and HR-192A. Always verify compatibility with your model before ordering.


Q4: What are the installation tips for this nozzle?

A:

  • Remove the high-speed screw before installation.
  • Align the nozzle’s side hole with the carb’s pick-off hole.
  • Never press-fit this threaded part into a non-threaded carb.


Q5: What causes fuel to leak at idle if this check valve is installed?

A: A leak at idle is usually due to a worn needle valve or leaking seat—not the check valve. Check those components if you're experiencing fuel leaks.


Q6: Can I use this on HL-series Tillotson carbs?

A: No. The 363-508 is threaded, and HL-series carbs often use press-in nozzles. Forcing this part into a non-threaded carb may cause damage.

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