How to Make Timing Adjustments on a 1976 25 HP Mercury Outboard

With the wear and tear of years of recreational boating, the devices used to control your boat's power and acceleration can need adjustment. If you've recently purchased a used motor, are experiencing problems with your boat's acceleration or are performing routine maintenance on your boat, you may want to check and adjust the timing.

Difficulty: Moderate

Instructions

Things You'll Need:

• Spark plug gap tool
• Timing light
• Dial indicator

Adjust the Timing Belt

1. Find the flywheel. The flywheel is inside the power head, which can be found by removing the cowling cover.

2. Install the dial indicator. Remove the spark plugs and attach the dial indicator to the top spark plug hole.

3. Adjust the timing belt. Rotate the flywheel clockwise until the #1 piston is at top center. Set the dial indicator at 0. Slowly rotate the flywheel counter clockwise until the dial indicator needle is at the 0.464 mark. Now, rotate the flywheel clockwise until the dial indicator is at 0.464.

4. Remove the dial indicator, replace the spark plugs and place the cowling cover back over the power head.

Adjust the Ignition Timing

5. Remove the spark plugs and install a temporary spark gap tool.

6. Detach the throttle cable from the power head and attach your timing light to the first lead.

7. Adjust the idle timing. Shift into neutral, hold the throttle arm, and start the engine. Adjust the idle timing screw to 2 degrees before top center. Turn off the engine.

8. Adjust the wide-open throttle timing. Shift into neutral, hold the throttle arm and start the engine. Adjust the maximum timing screw to 24 degrees before top center. Turn off the engine.

9. Turn off the engine and securely replace all your equipment.

Tips & Warnings

• If you're unfamiliar with the parts of your outboard motor, read your owner's manual in order to better familiarize yourself with them. You must use a dial indicator in order to get the proper alignment. Timing cannot be adjusted without a dial indicator.

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