6G9-85540 CDI Unit for Yamaha Mercury | JLM Marine

CDI Unit for Yamaha Mercury 4-Stroke Outboard 8HP 9.9HP | Direct Replacement for 6G9-85540

This aftermarket CDI (Capacitor Discharge Ignition) unit is engineered to fit Yamaha 9.9 HP 2-cylinder engines (1985–2005) and Mercury/Mariner 8 HP and 9.9 HP 2-cylinder 4-stroke outboards (1995–2000). It delivers reliable ignition performance across a wide range of model years for both brands.

This unit directly replaces Yamaha 6G9-85540-20-00, 6G9-85540-21-00, 6G9-85540-22-00, 6G9-85540-29-00, and Mercury 825667, 825667T, ensuring seamless compatibility with your existing electrical system.

• Fits both Yamaha and Mercury 2-cylinder 4-stroke outboards
• Direct plug-and-play replacement for OEM ignition packs
• Covers multiple model years from mid-1980s to mid-2000s

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Yamaha owners, here's a guide to help you identify your engine's serial/model: Yamaha Serial Number Guide. You can also review exploded diagrams to verify part numbers: Yamaha Parts Diagrams & Catalog.

For Mercury owners, here's a guide to help you identify your engine's serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 × CDI Unit for Yamaha Mercury 4-Stroke Outboard 8HP 9.9HP

Installation Guide

1. Disconnect the battery: Remove the negative cable to ensure all electrical power is off before beginning work.
2. Locate the existing CDI unit: It is typically mounted near the engine block or under the cowling. Consult your service manual if unsure.
3. Disconnect wiring harness: Carefully unplug all connectors from the old CDI unit. Note the wire colors and positions for reference.
4. Remove mounting hardware: Unbolt or unclip the old CDI unit from its bracket.
5. Install the new CDI unit: Position the replacement unit in the same location and secure it with the original mounting hardware.
6. Reconnect wiring harness: Attach all connectors to the new CDI unit, ensuring each plug is fully seated and secure.
7. Reconnect the battery: Reattach the negative cable and ensure all connections are tight.
8. Test the ignition system: Turn the key to the ON position and attempt to start the engine. Verify smooth ignition and consistent running.
9. Check for error codes: If your engine has a diagnostic system, confirm no fault codes are present.
10. Perform a sea trial: Run the engine at various RPMs to ensure stable performance and proper timing under load.

Troubleshooting & FAQ

How do I confirm this CDI unit fits my engine?
Check the compatibility table above for your engine's brand, HP, and year range. Cross-reference your original part number (6G9-85540 series for Yamaha or 825667/825667T for Mercury) to ensure a match.

What are the signs that my CDI unit is failing?
Common symptoms include hard starting, intermittent misfires, loss of power at high RPM, or complete failure to spark. If you've ruled out spark plugs and coils, the CDI unit is often the next component to check.

How often should I replace the CDI unit?
CDI units typically last many years under normal use. Replace only if you experience ignition problems or if diagnostics point to CDI failure. There is no fixed maintenance interval.

Will this aftermarket CDI perform the same as the OEM unit?
Yes. This unit is built to OEM specifications and delivers equivalent ignition performance. It is tested to ensure reliable spark timing and durability across the full RPM range.

Can I install this CDI unit myself?
If you have basic mechanical and electrical skills, installation is straightforward—disconnect the old unit, swap in the new one, and reconnect the wiring. However, professional installation is recommended to avoid incorrect wiring or damage.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.