* Fuel System Issues: This is a very common cause.
* Dirty or clogged fuel filter: Restricting fuel flow, especially noticeable at idle when fuel demand is lower.
* Bad fuel pump: Not delivering enough fuel pressure.
* Clogged carburetor jets (if carbureted): Small passages can become clogged with dirt or varnish, restricting fuel flow.
* Water in the fuel: Can cause sputtering and poor performance.
* Bad fuel: Old, stale, or contaminated fuel.
* Ignition System Problems:
* Spark plug issues: Fouled, worn, or improperly gapped spark plugs.
* Weak spark: Problems with the ignition coil, distributor (if applicable), or wiring.
* Air Intake:
* Clogged air filter: Restricting airflow to the engine.
* Other Potential Issues:
* Low compression: Worn piston rings or other internal engine damage.
* Vacuum leaks: Air leaking into the intake manifold can disrupt the air-fuel mixture.
* Throttle linkage problems: Could be misadjusted or sticking.
* Dirty or sticking throttle plates (if carbureted): Prevents the engine from idling smoothly.
Troubleshooting Steps (Proceed with caution and consult a Mercury repair manual):
1. Check the basics: Start with the easiest things to check. Inspect the spark plugs, air filter, and fuel filter. Replace them if necessary.
2. Check for fuel delivery: Ensure the fuel tank is full and the fuel lines are clear. If possible, check the fuel pressure.
3. Listen for unusual noises: A knocking or rattling sound could indicate internal engine problems.
4. Inspect the carburetor (if carbureted): This often requires cleaning or rebuilding.
5. Check for vacuum leaks: Use a carb cleaner spray to check for leaks around intake manifold gaskets and other connections. A hissing sound will indicate a leak.
Important Note: If you're not comfortable working on outboard motors, it's best to take your Mercury to a qualified marine mechanic. Improper repairs can lead to further damage or injury. They have the tools and expertise to properly diagnose and fix the problem.
