Quick Change Secondary Spring Kit

The Holley Quick Change Secondary Spring Kit (HLY20-59) is a precision carburetor tuning component engineered for rebuilds and performance adjustments on Holley carburetors. As a mechanic, you know that secondary spring tension directly controls the engagement point and modulation of the secondary throttle plates—critical for smooth transition from primary to secondary circuits. This quick-change design eliminates the need for permanent installation or complex spring swaps, allowing tuners to dial in the exact response curve your engine demands without carburetor disassembly.

Constructed from durable black plastic, the diaphragm cover housing protects the secondary spring assembly and maintains consistent spring preload under thermal cycling. The quick-change mechanism enables field testing and fine-tuning of secondary activation—whether you're running street fuel economy tests or dialing in a race carb for peak mid-range power delivery. Spring tension directly affects how aggressively the secondaries open; lighter springs engage sooner (improving bottom-end response), while heavier springs delay opening for better low-rpm stability. The modular design means you can compare spring rates without waiting for a full rebuild, cutting tuning time significantly during carburetor development or troubleshooting.

This kit is essential for enthusiasts restoring classic Holley four-barrel carburetors, performance shops validating tuning packages, and engine builders optimizing throttle response for specific applications—from street rods and muscle cars to vintage race engines. The compact profile (3.55 x 2.8 x 3.8 inches) and light weight (0.28 lbs) integrate seamlessly into existing carburetor assemblies. Verify your Holley carburetor model number before ordering to ensure spring rate compatibility, as secondary tension specifications vary across Holley's product line. Quick installation and repeatability make this a must-have service component for any shop managing multiple Holley carburetors.