Holley Power Valve 125-85 | 8.5 Hg Single-Stage Standard Flow + Gasket

Holley Single-Stage Power Valve - Part #125-85

Ensure optimal fuel enrichment during acceleration with this genuine Holley 8.5 in. Hg power valve. This critical component operates vacuum-controlled enrichment in your carburetor's power circuit, opening at 8.5 inches of mercury to deliver additional fuel during heavy acceleration and full-throttle operation, preventing lean conditions and hesitation. Includes gasket for complete installation.

What's Included:

• 1x power valve (8.5 in. Hg rating)
• 1x gasket

Key Features:

• 8.5 in. Hg Rating: Opens at 8.5 inches of mercury vacuum for precise enrichment timing
• Single-Stage Design: Standard flow for most street performance applications
• Vacuum Operated: Automatically responds to engine load conditions
• Genuine Holley Quality: OEM-grade component for reliable performance
• Standard Flow: Balanced enrichment for typical performance engines
• Gasket Included: Complete installation kit for leak-free operation

Performance Benefits:

• Prevents lean conditions during acceleration and heavy load
• Eliminates hesitation and bogging under throttle
• Provides smooth, consistent power delivery
• Automatically enriches fuel mixture when engine vacuum drops
• Essential for proper carburetor performance and engine protection

Understanding Power Valves:

• Function: Adds fuel to the main circuit when engine vacuum drops below the valve's rating
• Vacuum Rating: The point (in inches of mercury) at which the valve opens
• Selection Rule: Typically use a valve rated at half your idle vacuum reading
• Common Ratings: Range from 2.5 to 10.5 in. Hg for different applications
• 8.5 Rating: Ideal for engines with 17-18 in. Hg idle vacuum (higher vacuum engines)

Ideal Applications:

• Street performance engines with mild camshafts and higher idle vacuum
• Engines with 17-18 in. Hg idle vacuum (use half of idle vacuum)
• Stock and near-stock street engines
• Replacing failed or damaged power valves
• Carburetor rebuilds and overhauls
• Troubleshooting lean acceleration conditions

When to Replace:

• During carburetor rebuild or overhaul
• If experiencing hesitation or stumbling during acceleration
• After engine backfire (can rupture power valve diaphragm)
• When changing camshafts or engine modifications affect idle vacuum
• If fuel leaks from the power valve area
• As preventive maintenance during carburetor service

Selection Tips:

• Measure idle vacuum with engine fully warmed and in gear (automatic) or neutral (manual)
• Divide idle vacuum reading by 2 to determine proper power valve rating
• Example: 17 in. Hg idle vacuum ÷ 2 = 8.5 in. Hg power valve
• Lower vacuum engines (big cams) need lower-rated valves (3.5-6.5 in. Hg)
• Higher vacuum engines (stock/mild cams) use higher-rated valves (8.5-10.5 in. Hg)

Technical Specifications:

• Part Number: 125-85
• Vacuum Rating: 8.5 inches of mercury (in. Hg)
• Type: Single-stage power valve
• Flow: Standard
• Includes: Gasket
• Application: Holley performance carburetors with power valve circuits
• Common Use: Engines with 17-18 in. Hg idle vacuum

Fast dispatch from our Perth warehouse. In-store pickup available for local customers.