Stihl Blower BG65 No-Spark Fix (5 Pro Troubleshooting Steps)

A Stihl BG65 blower that won’t spark is as useful as a screen door on a submarine! It’s frustrating, time-wasting, and often happens when you need the machine most. Don’t despair. I’ve wrestled with this exact problem on countless Stihl blowers, and I’m here to guide you through five pro-level troubleshooting steps to resurrect your BG65. This isn’t just a generic checklist; it’s a deep dive into the ignition system, packed with practical advice, hard-earned wisdom, and a few personal anecdotes to keep things interesting.

Diagnosing the Silent Spark: 5 Steps to Revive Your Stihl BG65

Before we get our hands dirty, let’s understand the culprit: the ignition system. A healthy spark is the heart of any two-stroke engine. Without it, your fuel-air mixture is just sitting there, doing nothing. The BG65’s ignition system relies on a magneto ignition system. The magneto generates a high-voltage electrical pulse to the spark plug, timed precisely to ignite the fuel-air mixture.

Here’s my battle plan, honed from years of experience in the field:

1. Spark Plug Inspection: The First Line of Defense

This is always my starting point. It’s the simplest check, and often the problem. I remember one particularly frustrating day, clearing leaves after a storm. My BG65 sputtered and died. After tearing half the engine apart, I sheepishly discovered a fouled spark plug. A simple cleaning and re-gapping would have saved me hours!

The Procedure:
1. Safety First: Disconnect the spark plug wire from the spark plug. Never work on an ignition system with the wire connected.
2. Extraction: Use a spark plug wrench (typically 19mm or 3/4 inch) to carefully remove the spark plug.
3. Visual Inspection: Examine the spark plug. Look for:
  - Cracks or Damage: Any cracks in the ceramic insulator are a red flag. Replace the plug immediately.
  - Fouling: Check for excessive carbon buildup (black and sooty), oil (wet and oily), or fuel (wet and smelling of gasoline). This indicates an improper fuel mixture, worn piston rings, or a faulty carburetor.
  - Electrode Condition: Inspect the center and ground electrodes. They should be clean and sharp, not rounded or excessively worn.
4. Cleaning (If Necessary): If the plug is fouled but otherwise in good condition, you can try cleaning it. Use a wire brush or spark plug cleaner to remove deposits. Be gentle!
5. Gapping: Use a spark plug gapping tool to ensure the gap between the center and ground electrodes is correct. For a Stihl BG65, the recommended spark plug gap is typically 0.5mm (0.020 inches). This is crucial for a strong spark. Too wide, and the spark won’t jump. Too narrow, and the spark will be weak.
6. Testing (Optional): A spark plug tester can verify the plug’s ability to spark under pressure.
7. Reinstallation: Carefully reinstall the spark plug, tightening it to the manufacturer’s recommended torque. Overtightening can damage the cylinder head. A good rule of thumb is to tighten it “finger tight” and then another quarter turn with the wrench.
8. Reconnection: Reconnect the spark plug wire securely.
Technical Details and Data Points:
- Spark Plug Type: The recommended spark plug for a Stihl BG65 is typically a NGK BPM8Y or equivalent. Using the correct spark plug is vital for optimal performance and engine longevity.
- Torque Specification: The recommended torque for spark plug installation in a Stihl BG65 is around 12-15 Nm (9-11 ft-lbs). Refer to your owner’s manual for the exact specification.
- Electrode Wear: Excessive electrode wear (rounding or erosion) indicates a worn spark plug and should be replaced. Replace the spark plug every 50-100 hours of operation, or annually, depending on usage.
- Fouling Analysis:
  - Dry, Black Soot: Indicates a rich fuel mixture (too much fuel, not enough air).
  - Wet, Oily Deposits: Indicates oil leaking into the combustion chamber (worn piston rings or valve seals).
  - Wet, Fuel-Smelling Deposits: Indicates a flooded engine or a faulty carburetor.
Personalized Insight: I’ve found that using a small dab of anti-seize compound on the spark plug threads prevents them from seizing in the cylinder head, especially in older machines.

2. Spark Plug Wire and Boot: Checking the Connection

The spark plug wire and boot are the unsung heroes of the ignition system. They deliver the high-voltage pulse from the ignition coil to the spark plug. A damaged wire or a corroded boot can interrupt this vital connection.

The Procedure:
1. Safety First: Disconnect the spark plug wire from the spark plug.
2. Visual Inspection:
  - Wire Condition: Inspect the wire for cracks, cuts, or abrasions. Any damage can cause the spark to leak to ground, resulting in a weak or nonexistent spark at the spark plug.
  - Boot Condition: Check the spark plug boot for cracks, tears, or looseness. A damaged boot can allow moisture to enter, causing corrosion and poor electrical contact.
  - Connection Security: Ensure the spark plug wire is securely connected to both the spark plug and the ignition coil. A loose connection can cause intermittent sparking or no spark at all.
3. Resistance Testing:
  - Use a multimeter to measure the resistance of the spark plug wire. The resistance should be within the manufacturer’s specified range. A significantly higher or lower resistance indicates a damaged wire. A typical resistance for a spark plug wire is between 5,000 and 15,000 ohms per foot.
4. Boot Inspection:
  - Check the metal connector inside the boot for corrosion. Clean it with a wire brush or electrical contact cleaner if necessary.
5. Replacement (If Necessary): If the wire or boot is damaged or the resistance is out of specification, replace the entire spark plug wire assembly.
Technical Details and Data Points:
- Wire Type: Spark plug wires are typically made of a carbon-impregnated core surrounded by insulation. This design provides high voltage insulation and minimizes radio frequency interference (RFI).
- Boot Material: Spark plug boots are typically made of silicone rubber, which is resistant to heat, oil, and chemicals.
- Corrosion Prevention: Applying a small amount of dielectric grease to the inside of the spark plug boot can help prevent corrosion and improve electrical contact.
Personalized Insight: I once spent hours chasing a “no spark” issue on a Stihl chainsaw, only to discover that the spark plug wire had a tiny pinhole in the insulation, causing the spark to ground out against the engine block. A visual inspection under good lighting is crucial.

3. Ignition Coil Examination: The Spark Generator

The ignition coil is the heart of the ignition system. It transforms the low-voltage electrical current from the magneto into the high-voltage pulse needed to create a spark at the spark plug. A faulty ignition coil is a common cause of “no spark” issues.

The Procedure:
1. Safety First: Disconnect the spark plug wire from the spark plug.
2. Visual Inspection:
  - Coil Condition: Inspect the ignition coil for cracks, burns, or other damage. Any visible damage indicates a faulty coil.
  - Wiring Condition: Check the wiring connections to the ignition coil for corrosion or loose connections. Clean or tighten as necessary.
3. Air Gap Adjustment:
  - The air gap between the ignition coil and the flywheel is critical for proper operation. The air gap should be within the manufacturer’s specified range. For a Stihl BG65, the air gap is typically between 0.2mm and 0.4mm (0.008 inches and 0.016 inches). Use a feeler gauge to measure and adjust the air gap.
4. Resistance Testing:
  - Use a multimeter to measure the primary and secondary resistance of the ignition coil. The resistance should be within the manufacturer’s specified range. A significantly higher or lower resistance indicates a faulty coil. Refer to the Stihl BG65 service manual for the exact resistance specifications.
5. Spark Test (Using a Spark Tester):
  - Connect a spark tester between the ignition coil and the spark plug. Crank the engine and observe the spark. A weak or nonexistent spark indicates a faulty coil.
6. Replacement (If Necessary): If the ignition coil is damaged, the air gap cannot be adjusted properly, or the resistance is out of specification, replace the ignition coil.
Technical Details and Data Points:
- Coil Type: The ignition coil in a Stihl BG65 is typically a solid-state electronic ignition coil.
- Air Gap Importance: The air gap is critical because it affects the strength and timing of the spark. Too large of an air gap can result in a weak spark, while too small of an air gap can cause the coil to overheat and fail.
- Resistance Values: The primary resistance of the ignition coil is typically very low (less than 1 ohm), while the secondary resistance is much higher (several thousand ohms). Refer to the Stihl BG65 service manual for the exact resistance specifications.
Personalized Insight: I once encountered a BG65 with a perfectly good-looking ignition coil that refused to spark. It turned out that the coil was internally shorted, but the damage wasn’t visible. That’s why resistance testing is so important.

4. Flywheel and Key Inspection: Timing is Everything

The flywheel and key work together to ensure the ignition system fires at the correct time. The flywheel houses magnets that induce a current in the ignition coil as it spins. The key aligns the flywheel correctly on the crankshaft. A sheared or damaged flywheel key can throw off the timing, resulting in a “no spark” condition.

The Procedure:
1. Safety First: Disconnect the spark plug wire from the spark plug.
2. Accessing the Flywheel: Remove the blower housing and any other components that obstruct access to the flywheel.
3. Visual Inspection:
  - Flywheel Key: Inspect the flywheel key (also known as a woodruff key) for damage. A sheared or partially sheared key is a common cause of timing problems.
  - Flywheel Condition: Check the flywheel for cracks, damage, or loose magnets.
  - Crankshaft Condition: Inspect the crankshaft for damage or wear where the flywheel key sits.
4. Flywheel Removal (If Necessary): If the flywheel key is damaged or you need to inspect the flywheel more closely, you may need to remove the flywheel. Use a flywheel puller tool to remove the flywheel safely. Do not attempt to pry the flywheel off, as this can damage the crankshaft.
5. Key Replacement (If Necessary): If the flywheel key is damaged, replace it with a new key. Ensure the new key is the correct size and type for the Stihl BG65.
6. Flywheel Reinstallation: Reinstall the flywheel, aligning the keyway in the flywheel with the key on the crankshaft. Tighten the flywheel nut to the manufacturer’s specified torque.
7. Air Gap Adjustment (Revisited): After reinstalling the flywheel, recheck and adjust the air gap between the ignition coil and the flywheel.
Technical Details and Data Points:
- Key Material: Flywheel keys are typically made of soft metal, such as aluminum or brass, so they will shear under excessive stress to protect the engine.
- Flywheel Magnet Strength: The strength of the magnets in the flywheel is critical for generating a strong spark. Over time, the magnets can lose their strength, resulting in a weak spark.
- Torque Specification: The recommended torque for the flywheel nut on a Stihl BG65 is typically around 50-60 Nm (37-44 ft-lbs). Refer to your owner’s manual for the exact specification.
Personalized Insight: I once worked on a chainsaw that had a slightly bent crankshaft. The flywheel appeared to be installed correctly, but the timing was still off. It took me a while to diagnose the bent crankshaft, which was causing the flywheel to wobble slightly.

5. Kill Switch and Wiring: The Unexpected Interrupter

The kill switch is designed to ground out the ignition system, stopping the engine. A faulty kill switch or damaged wiring can inadvertently ground out the ignition system, preventing the engine from starting. This is often overlooked, but it’s a simple check that can save you a lot of time.

The Procedure:
1. Safety First: Disconnect the spark plug wire from the spark plug.
2. Kill Switch Inspection:
  - Visual Inspection: Check the kill switch for damage or corrosion.
  - Continuity Testing: Use a multimeter to test the continuity of the kill switch in both the “on” and “off” positions. In the “on” position (engine running), the kill switch should have no continuity (open circuit). In the “off” position (engine stopped), the kill switch should have continuity (closed circuit).
3. Wiring Inspection:
  - Visual Inspection: Check the wiring from the kill switch to the ignition coil for damage, corrosion, or loose connections.
  - Continuity Testing: Use a multimeter to test the continuity of the wiring from the kill switch to the ignition coil. Ensure there are no breaks or shorts in the wiring.
4. Disconnecting the Kill Switch (For Testing):
  - If you suspect a faulty kill switch or wiring, disconnect the kill switch wire from the ignition coil. This will eliminate the kill switch as a potential cause of the “no spark” issue. Try starting the engine. If the engine starts, the kill switch or wiring is the problem.
Technical Details and Data Points:
- Switch Type: The kill switch is typically a simple single-pole, single-throw (SPST) switch.
- Wiring Color Codes: Stihl typically uses specific color codes for the wiring in their equipment. Refer to the Stihl BG65 service manual for the wiring diagram and color codes.
- Corrosion Prevention: Applying a small amount of dielectric grease to the electrical connections can help prevent corrosion.
Personalized Insight: I once spent hours troubleshooting a “no spark” issue on a Stihl trimmer, only to discover that a mouse had chewed through the kill switch wire. The damage was hidden under the engine shroud, and I didn’t find it until I thoroughly inspected the wiring.

Beyond the Spark: Ensuring Optimal Performance

While getting the spark back is crucial, it’s only half the battle. To ensure your Stihl BG65 runs smoothly and efficiently, consider these additional factors:

Fuel System Examination

A clean and properly functioning fuel system is essential for a healthy engine. Check the fuel filter, fuel lines, and carburetor for any blockages or damage. Old fuel can also cause problems, so always use fresh fuel mixed with the correct ratio of two-stroke oil. Stihl recommends a fuel-to-oil ratio of 50:1 for their two-stroke engines. Using the wrong fuel mixture can lead to engine damage.

Air Filter Maintenance

A clean air filter allows the engine to breathe properly. A dirty air filter restricts airflow, causing the engine to run rich and lose power. Clean or replace the air filter regularly, depending on the operating conditions. I typically clean mine after every 5-10 hours of use.

Exhaust System Inspection

A clogged exhaust port or muffler can restrict exhaust flow, causing the engine to overheat and lose power. Inspect the exhaust port and muffler for carbon buildup and clean them as necessary.

Data-Backed Content and Unique Insights

Here’s some data-backed content and unique insights that I’ve gathered over the years:

Wood Moisture Content and Firewood: The ideal moisture content for firewood is 20% or less. Wood with a moisture content above 20% will be difficult to light, produce less heat, and create more smoke. I use a moisture meter to check the moisture content of my firewood before burning it.
Log Dimensions and Cord Volume: A standard cord of firewood is 4 feet high, 4 feet wide, and 8 feet long, totaling 128 cubic feet. The diameter of the logs will affect the stacking density and the actual amount of wood in the cord. Smaller logs will pack tighter than larger logs.
Chainsaw Calibration and Performance Metrics: Chainsaw chain sharpness is critical for efficient cutting. A dull chain will require more force to cut, increasing the risk of kickback and reducing cutting speed. I sharpen my chainsaw chain every 2-3 hours of use.
Wood Strength and Drying Tolerances: Hardwoods, like oak and maple, are denser and stronger than softwoods, like pine and fir. Hardwoods also take longer to dry. The drying time for firewood depends on the type of wood, the climate, and the stacking method. I typically allow hardwoods to dry for at least one year before burning them.
Industry Standards and Forestry Regulations: Always follow local forestry regulations and safety standards when working with chainsaws and other logging tools. Wear appropriate personal protective equipment (PPE), including a helmet, eye protection, hearing protection, gloves, and chainsaw chaps.

Case Study: Reviving a Neglected BG65

I once acquired a neglected Stihl BG65 from a friend who had left it sitting in his shed for years. The engine was completely seized, and the blower wouldn’t start. Here’s what I did to revive it:

Initial Assessment: The engine was seized, and the spark plug was heavily corroded.
Engine Disassembly: I disassembled the engine and found that the piston was stuck in the cylinder due to rust and corrosion.
Cleaning and Reconditioning: I cleaned the piston and cylinder with penetrating oil and fine steel wool. I also replaced the piston rings.
Ignition System Overhaul: I replaced the spark plug, spark plug wire, and ignition coil.
Fuel System Cleaning: I cleaned the carburetor, fuel filter, and fuel lines.
Reassembly and Testing: I reassembled the engine and tested it. The engine started on the first pull and ran smoothly.

The key to reviving this neglected BG65 was patience and attention to detail. I took my time to clean and recondition each component, ensuring that everything was in good working order.

Conclusion

Troubleshooting a “no spark” issue on a Stihl BG65 can be challenging, but with a systematic approach and a little patience, you can usually diagnose and fix the problem yourself. Remember to start with the simplest checks, such as the spark plug and spark plug wire, and work your way through the more complex components, such as the ignition coil and flywheel. And always prioritize safety. By following the steps outlined in this guide, you’ll be able to get your Stihl BG65 back up and running in no time, saving you time and money. Now, get out there and get blowing!