Surging is typically a sign of an issue with the mower’s fuel or air systems, but it could also involve engine components. Husqvarna mowers are built for reliability, so this problem is often fixable with some troubleshooting.
In this post, we’ll explore the common causes of surging, how to diagnose them, and practical steps to get your mower running smoothly again.
Why Is My Husqvarna Lawn Mower Surging
1. Clogged or Dirty Air Filter
A common cause of surging is a clogged air filter. The air filter ensures clean air enters the engine for combustion. Over time, dirt, grass clippings, and debris can build up, restricting airflow.
This creates a rich air-fuel mixture (too much fuel, not enough air), leading to surging as the engine struggles to maintain consistent performance.
Solution: Locate the air filter, usually on the side of the engine. Remove it and check for dirt or clogs. For foam filters, wash with warm, soapy water, dry thoroughly, and re-oil lightly. For paper filers, tap out loose debris or replace it if heavily soiled.
Husqvarna recommends replacing the air filter annually or after 25 hours of use. Regular cleaning or replacement can prevent this issue.
2. Fuel System Problems
Issues in the fuel system are another frequent cause of surging. If the engine isn’t getting a steady fuel supply, it can cause RPM fluctuations. Here are some fuel-related issues to consider:
- Stale or Old Fuel: Gasoline degrades over time, especially if left in the mower during the off-season. Stale fuel can clog the carburetor, leading to uneven engine performance.
- Clogged Fuel Line or Filter: Debris in the fuel line or a dirty fuel filter can restrict fuel flow, causing the engine to starve intermittently.
- Dirty Carburetor: The carburetor mixes air and fuel for combustion. Dirt or varnish from old fuel can disrupt this process, causing surging.
Solution: Start by draining old fuel and refilling with fresh, high-quality gasoline, ideally ethanol-free to avoid moisture and corrosion issues. Check the fuel filter (often an in-line component) and replace it if dirty.
If surging persists, clean the carburetor with a carburetor cleaner spray. For heavy buildup, a professional carburetor rebuild may be necessary.
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3. Blocked Fuel Cap Vent
A clogged fuel cap vent can also cause surging. The vent allows air to enter the fuel tank to replace used fuel. If it’s blocked, a vacuum forms, restricting fuel flow and causing the engine to surge.
Solution: Remove the fuel cap and inspect the vent (usually a small hole or valve). Clean it with a small wire or compressed air. If the cap is damaged, replace it with a Husqvarna-compatible part to ensure proper venting.
4. Spark Plug Issues
A worn or fouled spark plug can lead to inconsistent ignition, causing the engine to surge. If the spark plug is dirty, worn out, or improperly gapped, it may not fire reliably.
Solution: Remove the spark plug and check for carbon buildup, oil deposits, or wear. Clean it with a wire brush or replace it with a new one (Husqvarna mowers typically use NGK or Champion plugs).
Set the gap to the manufacturer’s specification, usually around 0.03 inches. Replace the spark plug annually to maintain optimal performance.
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5. Governor System Malfunctions
Husqvarna mowers use a governor to regulate engine speed. If the governor is misadjusted or damaged, it may overcompensate, causing the engine to surge as it tries to stabilize RPM.
Solution: The governor is typically near the carburetor. Check for loose or damaged components. Adjusting the governor is a delicate process, so consult your mower’s manual or a professional technician to ensure proper calibration.
6. Vacuum Leaks
A vacuum leak in the intake system can introduce extra air, disrupting the air-fuel mixture and causing surging. Common causes include cracked hoses, loose connections, or worn gaskets around the carburetor or intake manifold.
Solution: Inspect hoses and connections for cracks or looseness. Tighten fittings and replace damaged parts. If the carburetor gasket is worn, it may need replacement, which could require professional assistance.
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Preventive Maintenance Tips
To prevent surging and keep your Husqvarna mower in top shape, follow these maintenance tips:
- Clean or Replace Filters Regularly: Check air and fuel filters every 25 hours of use or at the start of the mowing season.
- Use Fresh Fuel: Always use fresh, ethanol-free gasoline. Add a fuel stabilizer if storing the mower for over 30 days.
- Schedule Annual Tune-Ups: Replace the spark plug, oil, and filters yearly, and have the carburetor cleaned or inspected.
- Store Properly: Drain the fuel tank or use a stabilizer before off-season storage to prevent fuel degradation.
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FAQs
How to stop a lawn mower from surging?
- Clean or replace the carburetor: Dirt or old fuel can clog it.
- Check the fuel: Use fresh gasoline. Old fuel can cause problems.
- Clean or replace the air filter: A dirty filter can restrict airflow.
- Inspect the fuel line: Look for blockages or leaks.
- Adjust the governor spring: If it’s loose or damaged, the engine can surge.
- Check for vacuum leaks: Inspect all gaskets and connections around the carburetor.
How to fix a lawn mower revving up and down?
- Step 1: Replace the air filter if it’s dirty.
- Step 2: Drain and refill with fresh fuel.
- Step 3: Clean the carburetor or use a carburetor cleaner.
- Step 4: Tighten or replace the governor spring.
- Step 5: Make sure the fuel cap vent is clear (a clogged cap can create a vacuum).
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What are common issues with Husqvarna mowers?
- Starting problems (bad spark plug, old fuel, or carburetor issues)
- Surging engine (as described above)
- Drive system failure in self-propelled models
- Blade engagement issues
- Uneven cutting (due to dull blades or unbalanced decks)
- Battery issues (for electric/start models)
- Deck belt slipping or breaking
Regular maintenance helps avoid many of these.
What causes a lawn mower to surge up and down?
- Dirty carburetor or jets
- Blocked fuel line or dirty fuel
- Dirty air filter
- Leaking or broken vacuum lines
- Bad or weak governor spring
- Clogged fuel cap vent
What are the symptoms of engine surge?
- Engine speed fluctuates without touching the throttle
- Revving up and down at idle or underload
- Unstable engine sound
- Poor performance or loss of power
- Increased fuel use or smoke
Final words
A surging Husqvarna lawn mower is a common issue that’s often fixable with basic troubleshooting. By checking the air filter, fuel system, spark plug, and other components, you can usually resolve the problem yourself. Regular maintenance is the best way to prevent surging and ensure your mower runs smoothly season after season. With a little care, your Husqvarna will be back to delivering a clean, even cut in no time.
