Briggs And Stratton Lawn Mower Surging

Quick Takeaway:

• Briggs and Stratton lawn mower surging is typically caused by fuel flow issues or air imbalance problems
• Most surging issues can be resolved with carburetor cleaning or adjustment
• Regular maintenance prevents many common surging problems
• Professional help may be needed for complex issues involving governor systems or internal engine components

The frustrating issue of a Briggs and Stratton lawn mower surging—where the engine repeatedly revs up and down instead of maintaining steady power—is usually caused by fuel delivery problems, carburetor issues, or air intake imbalances. Most surging problems can be fixed with basic maintenance like cleaning the carburetor, replacing the fuel, or adjusting key components.

What Causes a Briggs and Stratton Lawn Mower to Surge?

Nothing disrupts a peaceful Saturday morning mowing session quite like a lawn mower that won’t maintain a steady speed. If you’re dealing with a Briggs and Stratton lawn mower surging problem, you’re not alone. This common issue affects thousands of homeowners each year.

Surging (sometimes called “hunting”) occurs when your lawn mower engine repeatedly speeds up and slows down without any throttle adjustment. The mower seems to have a mind of its own—racing then sputtering in an endless cycle. This problem affects both push mowers and riding models equipped with Briggs and Stratton engines.

The most common causes of Briggs and Stratton engine surging include:

• Dirty or clogged carburetor
• Stale or contaminated fuel
• Blocked fuel cap vent
• Dirty air filter
• Improper governor adjustment
• Vacuum leaks
• Faulty fuel pump (on models with one)
• Damaged gaskets affecting air/fuel mixture

Understanding these root causes is the first step toward solving your Briggs and Stratton lawn mower surging issues. Let’s explore each potential cause and its solution in more detail.

Carburetor Problems: The #1 Culprit in Lawn Mower Surging

When troubleshooting a Briggs and Stratton lawn mower surging at idle or full throttle, the carburetor should be your first suspect. The carburetor is responsible for mixing air and fuel in the proper ratio for combustion. When this delicate balance is disrupted, surging often results.

How to Clean a Briggs and Stratton Carburetor

1. Gather supplies: You’ll need screwdrivers, carburetor cleaner spray, compressed air, and possibly a carburetor rebuild kit.

2. Access the carburetor: Remove the air filter cover and air filter to expose the carburetor.

3. Remove the carburetor: Disconnect the fuel line, throttle linkage, and mounting bolts to remove the carburetor from the engine.

4. Clean thoroughly: Spray carburetor cleaner through all passages and orifices. Pay special attention to the main jet and idle jet, as these tiny holes often get clogged.

5. Clear the idle circuit: This small passage is often overlooked but is a common source of surging at idle.

6. Inspect the float and needle valve: Make sure the float moves freely and the needle valve isn’t stuck or worn.

7. Reassemble carefully: Replace any worn gaskets and ensure all parts are properly positioned.

Many Briggs and Stratton lawn mower surging problems are resolved with a thorough carburetor cleaning. If you’ve tried cleaning and still experience issues, a carburetor replacement might be necessary, especially on older models where the parts have worn significantly.

Fuel-Related Issues Causing Engine Surging

Fuel problems are another major contributor to Briggs and Stratton lawn mower surging issues. Modern gasoline contains ethanol, which can absorb moisture and degrade over time.

How to Fix Fuel-Related Surging

1. Drain old fuel: If your mower has been sitting for more than 30 days, drain the old fuel completely.

2. Use fresh fuel: Refill with fresh gasoline that has an octane rating of 87 or higher.

3. Add fuel stabilizer: For longer storage periods, add a quality fuel stabilizer to prevent ethanol-related problems.

4. Check the fuel cap: A clogged vent in the fuel cap can create a vacuum in the tank, restricting fuel flow and causing surging. Clean the vent or replace the cap if necessary.

5. Inspect fuel lines: Cracked or clogged fuel lines can cause intermittent fuel delivery, leading to surging. Replace any damaged lines.

6. Examine the fuel filter: A partially clogged fuel filter can restrict flow, especially at higher RPMs. Replace if dirty or clogged.

Fuel-related issues are particularly common in Briggs and Stratton engines that sit unused for extended periods, such as over winter storage. Regular fuel system maintenance can prevent many of these problems.

Air Flow Problems That Cause Lawn Mower Surging

The air-fuel mixture in your Briggs and Stratton engine must be precisely balanced for smooth operation. When air flow is restricted or excessive, surging commonly occurs.

Fixing Air Flow Issues

1. Clean or replace the air filter: A dirty air filter restricts air flow, creating a rich fuel mixture that causes surging. Check your air filter and clean or replace it as needed.

2. Inspect the choke: A stuck choke plate can restrict air flow. Make sure the choke opens and closes properly, and that the automatic choke system (if equipped) functions correctly.

3. Check for vacuum leaks: Cracks in intake manifolds or loose connections can allow unmetered air into the engine, disrupting the air-fuel ratio. Inspect all gaskets and seals between the carburetor and engine.

4. Examine the breather tube: A clogged or damaged breather tube can cause pressure imbalances leading to surging.

Many homeowners overlook air flow problems when troubleshooting a Briggs and Stratton engine running rough, but these issues are just as important as fuel delivery in preventing surging.

Governor System Problems and Adjustments

The governor on your Briggs and Stratton engine helps maintain a consistent speed regardless of load changes. When the governor system malfunctions, surging can result.

Troubleshooting Governor Issues

1. Check for binding: Ensure the governor linkage moves freely without sticking or binding.

2. Inspect for damage: Look for bent, broken, or disconnected linkage components.

3. Make proper adjustments: If your governor is adjustable, follow the specifications in your engine manual. Typically, this involves:

   • Locating the governor adjustment screw
   • Loosening the clamping nut
   • Turning the screw clockwise to increase sensitivity (which can reduce surging)
   • Retightening the clamping nut

4. Check the governor spring: A stretched or damaged governor spring can cause erratic engine behavior.

Governor issues are more common on older Briggs and Stratton engines or those that have been disassembled for service. If you recently performed maintenance on your mower, double-check all governor connections and adjustments.

For complex governor problems on models like the Briggs and Stratton Intek V-twin, professional service might be required.

Advanced Troubleshooting for Persistent Surging Issues

If you’ve addressed the common causes above and your Briggs and Stratton lawn mower is still surging, it’s time to look at some less common but potential culprits.

Less Common Causes of Surging

1. Valve issues: Improper valve clearance can cause surging, especially at certain RPM ranges. Check valve clearance according to your engine specifications.

2. Ignition problems: While less common, faulty spark plugs, ignition coils, or timing issues can sometimes manifest as surging.

3. Compression problems: Low compression in one cylinder (on twin-cylinder models) can cause uneven running that resembles surging.

4. Electronic fuel management issues: Some newer Briggs and Stratton engines use electronic fuel management systems that can malfunction and cause surging.

5. Exhaust restrictions: A partially clogged muffler can cause back pressure in the engine, leading to surging.

If your 24 hp Briggs and Stratton engine surging problem persists after trying all these solutions, it may be time to consult with a qualified small engine repair specialist.

DIY vs. Professional Repair: When to Call a Pro

Many Briggs and Stratton lawn mower surging issues can be fixed at home with basic tools and mechanical knowledge. However, some problems are best left to professionals.

Consider Professional Help When:

• You’ve tried all common solutions without success
• Your mower has a complex electronic fuel injection system
• The engine has internal mechanical problems
• You lack the tools or confidence to disassemble engine components
• The mower is under warranty (DIY repairs might void it)

Professional small engine mechanics have specialized tools and diagnostic equipment to identify problems quickly. They also have access to genuine Briggs and Stratton parts that might be difficult to source elsewhere.

For most homeowners, it makes sense to try the basic troubleshooting steps before paying for professional service. Start with the easiest and most common fixes like cleaning the carburetor and replacing the fuel.

Preventing Future Briggs and Stratton Surging Problems

Prevention is always easier than cure. Here are some maintenance practices to prevent future surging issues:

1. Use fuel stabilizer: Add fuel stabilizer to your gas can each time you fill up, especially if you don’t use your mower weekly.

2. Drain fuel for storage: Before winter storage, either drain the fuel system completely or fill the tank with stabilized fuel.

3. Perform regular maintenance: Follow your owner’s manual schedule for air filter cleaning, oil changes, and spark plug replacement.

4. Run the engine regularly: Even during off-seasons, start your mower and let it run for 15 minutes every month if possible.

5. Clean the carburetor annually: Even if your mower isn’t showing problems, an annual carburetor cleaning prevents buildup.

6. Use quality fuel: Higher octane fuel without ethanol (when available) can prevent many common fuel-related issues.

These preventative measures can significantly reduce the likelihood of dealing with a Briggs and Stratton lawn mower surging problem in the future.

Common Problems with Specific Briggs and Stratton Models

Different Briggs and Stratton engine models can exhibit specific surging patterns or have unique troubleshooting requirements.

17.5 HP Intek Engines

The 17.5 HP Intek engines commonly experience surging related to their carburetor design. The fixed main jet can easily become clogged with the smallest amount of debris. When troubleshooting these engines:

• Pay special attention to the main jet cleaning
• Check the bowl gasket for proper sealing
• Inspect the emulsion tube for partial blockages

20-25 HP V-Twin Engines

Higher horsepower V-twin engines, like those found on many riding mowers, often experience surging related to their dual-carburetor systems or fuel pumps. For these engines:

• Ensure both carburetors are clean and synchronized
• Check the pulse-operated fuel pump for proper operation
• Verify that both cylinders have good compression

If you’re dealing with V-twin specific issues, specialized troubleshooting might be required.

FAQ: Briggs and Stratton Lawn Mower Surging Issues

What can cause surging on a Briggs and Stratton motor?

Surging is typically caused by fuel delivery problems, carburetor issues, dirty air filters, or governor malfunctions. The most common culprit is a dirty carburetor with partially clogged jets that create an inconsistent fuel flow, causing the engine to repeatedly rev up and down.

How do I fix my Briggs and Stratton engine surging?

Start by cleaning the carburetor, replacing the fuel with fresh gasoline, and checking the air filter. If these steps don’t resolve the issue, inspect the fuel cap vent, check for vacuum leaks, and examine the governor linkage for proper operation and adjustment.

Why does my lawnmower hunt and surge?

“Hunting” or surging occurs when the engine can’t maintain a steady RPM due to fluctuating fuel or air supply. This is commonly caused by partially clogged carburetor passages creating an inconsistent fuel flow, resulting in alternating rich and lean conditions as the engine runs.

How do I fix my lawn mower revving up and down?

Clean the carburetor thoroughly, focusing on the idle circuit and main jet. Replace old fuel with fresh gasoline, check for a clogged fuel cap vent, and ensure the governor linkage moves freely. For persistent issues, inspect vacuum lines and the integrity of gaskets between the carburetor and engine.

What causes surging at high RPM on my lawn mower?

Surging at high RPM often indicates restrictions in the main fuel jet or high-speed circuit of the carburetor. It can also be caused by a partially clogged fuel filter limiting flow during high demand, vacuum leaks becoming more pronounced at high RPM, or improper governor adjustment.

What is the most common reason why a Briggs & Stratton small engine won’t run correctly?

Fuel system issues—particularly carburetor problems—are the most common reason for Briggs & Stratton engine troubles. Modern fuel containing ethanol attracts moisture and leaves gummy deposits in carburetors when engines sit unused, leading to running problems like surging, stalling, or failure to start.

Why is my lawn mower surging with a new carburetor?

If your mower is surging with a new carburetor, check that it’s properly installed with correctly connected linkages, has the right jet sizes for your engine model, and that no gaskets are pinched or damaged. Also verify the governor is correctly connected and adjusted, as improper setup can cause surging even with new parts.

Final Words: Conquering Your Briggs and Stratton Surging Issues

Dealing with a Briggs and Stratton lawn mower surging problem can be frustrating, but with the right approach, it’s typically a fixable issue. Most surging problems stem from fuel delivery issues that can be resolved with basic maintenance and cleaning.

Remember that regular maintenance prevents many common surging issues. By keeping your carburetor clean, using fresh fuel, and checking air filters regularly, you can avoid the headache of a surging engine and enjoy smooth mowing all season long.

If you’ve tried the solutions in this guide without success, don’t hesitate to consult with a qualified small engine technician who specializes in Briggs and Stratton engines. Sometimes, a professional diagnosis can save you time and frustration in the long run.

Happy mowing!