291337001 Ignition Coil & Spark Plug Kit 

Key Features

• High-Energy Spark Output: Precision-wound internal coils generate a consistent, high-voltage pulse to ensure reliable ignition even in cold starts or high-load brush cutting conditions.
• Optimized Ignition Mapping: Specifically calibrated for Ryobi 25.4cc 2-cycle engines to provide efficient combustion, leading to smoother idling and improved throttle response.
• Weather-Shielded Encapsulation: The internal circuitry is fully potted in high-grade, heat-resistant epoxy to protect against vibration, moisture, and debris common in outdoor landscaping.
• Reinforced High-Tension Lead: Equipped with a durable silicone spark plug boot and a heavy-duty wire designed to resist electrical "arching" and thermal degradation.
• Complete Ignition Refresh: This kit includes both the electronic ignition module and a matched spark plug, providing a total solution for restoring a weak or non-existent spark.

Replaces / Cross-Reference Part Numbers

• 291337001
• 850108001
• PS16533515
• 985721001

Compatibility & Fitment

This ignition module is a standard replacement for the Ryobi and Homelite 25cc to 26cc "Full Crank" and "Half Crank" engine platforms. Key compatible models include:

• Ryobi String Trimmers: RY252CS, RY253SS, RY251PH, RY254BC.
• Ryobi Brush Cutters: Various models utilizing the 25cc 2-cycle engine chassis.
• Homelite Trimmers: Fits several 25cc/26cc handheld models that utilize the 291337001 part number.
• Note: Always verify your original coil's mounting hole spacing and wire orientation, as some newer 25cc models may utilize a different module configuration.

When to Replace

• No Spark Condition: The most common failure; the trimmer will not start despite having fresh fuel and a clean carburetor because the plug is not firing.
• Thermal Failure (Hot Stalling): The engine runs perfectly for 10–15 minutes but dies suddenly as it gets hot and refuses to restart until the coil cools down.
• Engine Misfiring: Rhythmic stuttering or "popping" at full throttle, indicating the coil is struggling to maintain a steady electrical pulse under load.
• Hard Starting: A weak spark requires excessive pulls on the starter cord to get the engine to fire, often leading to a flooded engine.
• Visible Insulation Damage: The spark plug wire is frayed or showing signs of being chewed by rodents, which can cause the spark to jump to the engine block instead of the plug.

Installation Tips

• The Air Gap Rule: For the strongest spark, the air gap between the coil legs and the flywheel magnets should be approximately 0.010" to 0.012". Use a standard business card as a feeler gauge during installation.
• Check the Ground Path: Ensure the mounting surfaces on the engine block and the coil legs are clean and free of rust or oil. The coil grounds through its mounting bolts; a weak ground will cause a weak spark.
• Kill Switch Wiring: Be careful when reconnecting the small spade terminal for the stop wire. If this wire is pinched or grounds against the engine housing, the engine will never start.
• Flywheel Magnet Cleanup: While the cover is off, use a rag to wipe away any metal shavings or debris from the flywheel magnets to ensure the strongest possible magnetic induction.
• Gap the Spark Plug: Before installation, verify the spark plug gap (typically 0.025") to ensure optimal combustion and to prevent unnecessary stress on the new ignition module.