Maintaining your Stihl weed eater is key to its longevity and performance. A crucial part of this maintenance is ensuring you use the correct spark plug. While Stihl has many models, a few spark plug types cover a wide range of their popular weed eaters.
Important Note: This chart is a general guide. The most accurate and up-to-date spark plug recommendation for your specific Stihl weed eater model will always be found in your owner’s manual or by consulting a Stihl dealer. Always verify the spark plug type before installation.
Understanding Stihl Spark Plugs (Common Types)
Stihl weed eaters primarily use two common types of spark plugs, often from NGK or Bosch:
- NGK BPMR7A (or Bosch WSR6F): This is a very common spark plug for many older and current 2-stroke Stihl trimmers. It’s often found in models like the FS38, FS45, FS55, FS85, FS120, FS250, and many others.
- NGK CMR6H (or Bosch USR7AC): This spark plug is typically used in newer Stihl models, especially those with 4-MIX engines, and some 2-stroke models designed for lower emissions. You’ll often find this in models like the FS56, FS70, FS90, FS100, FS110, FS130, FS240, and the KM series KombiMotors.
- NGK CMR5H or CMR7A: Some less common or very specific models might use these. For example, some FS83 models might use CMR7A, and some 4-stroke trimmers might use CMR5H.
General Stihl Weed Eater Spark Plug Cross-Reference Chart
| Stihl Weed Eater Series/Models (Examples) | Common NGK Spark Plug | Common Bosch Spark Plug (Cross-Reference) | Notes / Engine Type |
| FS 38, FS 45, FS 46, FS 55, FS 75, FS 80, FS 85, FS 120, FS 200, FS 250, FS 350, FS 450, FS 550, FS 560 | NGK BPMR7A | Bosch WSR6F | Primarily 2-stroke engines |
| FS 40 (new), FS 50, FS 56, FS 70, FS 90, FS 94, FS 100, FS 110, FS 130, FS 240, FS 251, FS 310, FS 360, FS 460 | NGK CMR6H | Bosch USR7AC | Often 4-MIX engines, or newer 2-stroke models |
| FS 83 | NGK CMR7A | Less common, always check manual | |
| FS 40 (old), FS 44 | NGK BMR6A | Older 2-stroke models | |
| Stihl Kombi-Motors (KM series): KM 55, KM 85 | NGK BPMR7A | Bosch WSR6F | Older 2-stroke Kombi-Motors |
| Stihl Kombi-Motors (KM series): KM 56, KM 90, KM 110, KM 130 | NGK CMR6H (some KM90/110 may use USR7AC also) | Bosch USR7AC | Often 4-MIX Kombi-Motors |
Spark Plug Gap: For most Stihl weed eaters, the recommended spark plug gap is typically around 0.020 inches (0.5 mm) or 0.028 inches (0.7 mm). Always refer to your owner’s manual for the exact specification for your model. An incorrect gap can lead to poor performance and starting issues.
Why the Right Spark Plug Matters
- Optimal Performance: The correct spark plug ensures efficient ignition, leading to better fuel economy, consistent power, and smooth operation.
- Easier Starting: A properly gapped and correct spark plug will make your weed eater easier to start, especially when cold.
- Engine Health: Using the wrong type of spark plug can lead to various issues, including misfires, carbon buildup, and even engine damage over time.
- Longevity: Replacing your spark plug at recommended intervals (usually annually or every 50 hours of use) helps prolong the life of your engine.
When to Replace Your Spark Plug
- Difficulty Starting: If your weed eater is hard to start, especially when warm.
- Rough Idling or Misfires: If the engine runs unevenly or “skips.”
- Loss of Power: If your trimmer seems to have less power than usual.
- Excessive Smoke: While often fuel-related, a fouled spark plug can contribute to this.
- Regular Maintenance: Even if none of the above symptoms are present, it’s good practice to replace the spark plug annually or every 50 hours of use as part of routine maintenance.
By using this guide and always double-checking your owner’s manual, you’ll be well-equipped to keep your Stihl weed eater in top-notch condition for all your landscaping needs!