Briggs & Stratton 675EX Engine Troubleshooting (5 Key Fixes)

Ever found yourself yanking the starter cord of your Briggs & Stratton 675EX engine, only to be met with stubborn silence? Or maybe it sputters to life, runs rough, and dies faster than a campfire in a downpour? If so, you’re in the right place. This engine, a workhorse found on countless lawnmowers, tillers, and other small equipment, is generally reliable. But like any machine, it can have its off days.

As a seasoned woodworker and small engine enthusiast, I’ve spent countless hours tinkering with these engines, coaxing them back to life. I’ve learned that a little know-how can save you a lot of frustration and money. In this article, I’ll share my hard-earned wisdom to help you troubleshoot the five most common problems with the Briggs & Stratton 675EX engine. We’ll dive deep into each issue, offering practical, step-by-step solutions that you can tackle in your own garage or workshop.

Briggs & Stratton 675EX Engine Troubleshooting: 5 Key Fixes

1. Fuel System Issues: When Your Engine Starves for Gas

A clean and properly functioning fuel system is the lifeblood of any small engine. If your 675EX engine is hard to start, stalls frequently, or runs erratically, the problem often lies within the fuel system.

The Culprits:
- Stale Fuel: Gasoline degrades over time, especially when mixed with ethanol. Ethanol attracts water, which can lead to corrosion and gumming up of the carburetor.
- Clogged Fuel Filter: The fuel filter prevents debris from entering the carburetor. A clogged filter restricts fuel flow, starving the engine.
- Dirty Carburetor: The carburetor mixes air and fuel in the correct ratio for combustion. Over time, varnish and deposits can build up in the carburetor’s jets and passages, disrupting this delicate balance.
- Faulty Fuel Lines: Cracked or damaged fuel lines can leak air or fuel, leading to poor engine performance.
- The Fixes:
- Drain and Replace Stale Fuel: This is the first and simplest step. If your engine has been sitting for a while, drain the old fuel and replace it with fresh gasoline. Consider using fuel stabilizer to extend the life of your fuel, especially if you don’t use the engine frequently. Fuel stabilizers can prevent fuel degradation for up to 24 months. In my experience, using a fuel stabilizer has saved me countless carburetor cleanings. I once left a lawnmower with untreated fuel sitting for six months, and the carburetor was so gummed up it took me an entire afternoon to clean!
- Replace the Fuel Filter: The fuel filter is an inexpensive part, and replacing it regularly is good preventative maintenance. I recommend replacing it at least once a year, or more often if you use the engine in dusty or dirty conditions. To replace the filter, simply disconnect the fuel lines from the old filter and connect them to the new one, ensuring that the filter is installed in the correct direction (there’s usually an arrow indicating fuel flow).
- Clean the Carburetor: Cleaning the carburetor can be a bit more involved, but it’s often necessary to restore proper engine performance. You can try using a carburetor cleaner spray, but for heavily gummed-up carburetors, a thorough disassembly and cleaning is required.
  - Carburetor Cleaning Steps:
    1. Disconnect the Fuel Line: Before starting, disconnect the fuel line from the carburetor to prevent fuel spillage.
    2. Remove the Carburetor: Carefully remove the carburetor from the engine. Take pictures as you disassemble it so you have a reference for reassembly.
    3. Disassemble the Carburetor: Disassemble the carburetor, removing the float bowl, float, needle valve, and jets. Be careful not to lose any small parts.
    4. Clean the Parts: Clean all the parts with carburetor cleaner, paying particular attention to the jets and passages. Use a small wire or carburetor cleaning tool to clear any blockages.
    5. Reassemble the Carburetor: Reassemble the carburetor, making sure all the parts are properly seated.
    6. Reinstall the Carburetor: Reinstall the carburetor on the engine and reconnect the fuel line.
  - Personal Story: I remember helping a neighbor who was ready to throw away his lawnmower because it wouldn’t start. After a thorough carburetor cleaning, the engine roared back to life, saving him the cost of a new mower. The satisfaction of breathing new life into old equipment is one of the things I love most about working with small engines.
    - Inspect and Replace Fuel Lines: Check the fuel lines for cracks, leaks, or damage. If you find any, replace them with new fuel lines of the correct size. Make sure the fuel lines are securely attached to the fuel filter, carburetor, and fuel tank.

2. Ignition System Issues: No Spark, No Start

The ignition system is responsible for creating the spark that ignites the air-fuel mixture in the cylinder. If your 675EX engine won’t start and you suspect a lack of spark, the following components are the most likely culprits:

The Culprits:
- Faulty Spark Plug: The spark plug is the heart of the ignition system. A fouled, cracked, or worn spark plug can prevent the engine from starting.
- Loose or Corroded Spark Plug Wire: The spark plug wire carries the electrical current from the ignition coil to the spark plug. A loose or corroded wire can disrupt the flow of electricity.
- Faulty Ignition Coil: The ignition coil generates the high-voltage electricity needed to create a spark. A faulty ignition coil can prevent the engine from starting.
- Low Oil Sensor Malfunction: Some 675EX engines have a low oil sensor that prevents the engine from starting if the oil level is too low. A malfunctioning sensor can prevent the engine from starting even if the oil level is sufficient.
- The Fixes:
- Check and Replace the Spark Plug: Remove the spark plug and inspect it for fouling, cracks, or wear. Clean the spark plug with a wire brush or replace it with a new one. Make sure the spark plug gap is set to the correct specification (usually around 0.030 inches). You can use a spark plug gap tool to ensure the correct gap. I always keep a spare spark plug on hand for each of my engines. It’s a cheap and easy way to troubleshoot ignition problems.
- Check the Spark Plug Wire: Inspect the spark plug wire for looseness, corrosion, or damage. Make sure the wire is securely connected to the spark plug and the ignition coil. If the wire is damaged, replace it with a new one.
- Test the Ignition Coil: Testing the ignition coil requires a multimeter. Disconnect the spark plug wire from the spark plug and connect the multimeter to the spark plug wire terminal and the engine ground. Crank the engine and check for a voltage reading. If there is no voltage reading, the ignition coil is likely faulty and needs to be replaced.
- Check the Low Oil Sensor: If your engine has a low oil sensor, check the oil level and make sure it is at the correct level. If the oil level is sufficient and the sensor is still preventing the engine from starting, try disconnecting the sensor. If the engine starts with the sensor disconnected, the sensor is faulty and needs to be replaced. Important Note: Disconnecting the low oil sensor bypasses the engine’s protection against low oil levels. Only do this for testing purposes and replace the sensor as soon as possible.

3. Compression Issues: Losing Power and Efficiency

Compression is the measure of how well the engine seals the combustion chamber. Low compression can lead to hard starting, loss of power, and reduced fuel efficiency.

The Culprits:
- Worn Piston Rings: Piston rings seal the gap between the piston and the cylinder wall. Over time, the rings can wear down, allowing combustion gases to leak past the piston, reducing compression.
- Worn Cylinder: The cylinder wall can also wear down over time, creating a gap between the piston and the cylinder wall.
- Leaking Valves: The valves seal the intake and exhaust ports. If the valves are worn or damaged, they can leak, reducing compression.
- Blown Head Gasket: The head gasket seals the cylinder head to the engine block. A blown head gasket can allow combustion gases to leak out, reducing compression.
- The Fixes:
- Compression Test: A compression test is the best way to diagnose compression problems. You’ll need a compression tester, which is a gauge that screws into the spark plug hole.
  - Compression Test Steps:
    1. Warm Up the Engine: Run the engine for a few minutes to warm it up.
    2. Remove the Spark Plug: Remove the spark plug from the cylinder you want to test.
    3. Install the Compression Tester: Screw the compression tester into the spark plug hole.
    4. Crank the Engine: Crank the engine for several seconds, watching the gauge on the compression tester.
    5. Record the Reading: Record the compression reading.
  - Interpreting the Results: A healthy 675EX engine should have a compression reading of around 75-100 PSI. If the reading is significantly lower than this, it indicates a compression problem.
    - Oil Test: If the compression test is low, you can perform an oil test to help pinpoint the source of the problem. Squirt a small amount of oil into the cylinder through the spark plug hole and repeat the compression test. If the compression reading increases, it indicates that the problem is likely with the piston rings or cylinder. If the reading doesn’t increase, the problem is likely with the valves or head gasket.
    - Valve Adjustment: Sometimes, low compression can be caused by improperly adjusted valves. Check the valve clearance and adjust it according to the engine manufacturer’s specifications.
    - Engine Overhaul: If the compression test indicates worn piston rings, a worn cylinder, or leaking valves, the engine may need to be overhauled. This is a more involved repair that typically requires specialized tools and knowledge.

4. Governor Issues: Erratic Engine Speed

The governor is a mechanical device that maintains a consistent engine speed under varying loads. If your 675EX engine surges, hunts, or runs erratically, the governor may be the culprit.

The Culprits:
- Loose or Damaged Governor Linkage: The governor linkage connects the governor to the carburetor throttle. If the linkage is loose or damaged, it can cause the engine speed to fluctuate.
- Weak or Broken Governor Spring: The governor spring provides the tension that controls the governor’s movement. If the spring is weak or broken, it can cause the engine speed to surge or hunt.
- Internal Governor Problems: In some cases, the governor itself may be damaged or worn, requiring replacement.
- The Fixes:
- Inspect the Governor Linkage: Check the governor linkage for looseness, damage, or binding. Make sure the linkage is properly connected to the governor and the carburetor throttle. Lubricate the linkage with a light oil.
- Check the Governor Spring: Inspect the governor spring for weakness or breakage. If the spring is weak or broken, replace it with a new one.
- Adjust the Governor: In some cases, the governor may need to be adjusted to maintain the correct engine speed. Consult the engine manufacturer’s service manual for instructions on how to adjust the governor.

5. Overheating Issues: When Your Engine Gets Too Hot

Overheating can cause serious damage to your 675EX engine. If your engine is overheating, it’s important to identify and address the problem quickly.

The Culprits:
- Dirty Cooling Fins: The cooling fins on the engine cylinder help to dissipate heat. If the fins are covered in dirt, debris, or grass clippings, they can’t effectively cool the engine.
- Low Oil Level: Oil not only lubricates the engine but also helps to cool it. Low oil levels can lead to overheating.
- Restricted Airflow: Anything that restricts airflow around the engine can cause it to overheat. This could be caused by a clogged air filter, a blocked cooling fan, or operating the engine in a confined space.
- Engine Overload: Overloading the engine by cutting thick grass or operating it under heavy load for extended periods can cause it to overheat.
- The Fixes:
- Clean the Cooling Fins: Regularly clean the cooling fins on the engine cylinder with a brush or compressed air.
- Check the Oil Level: Check the oil level regularly and add oil as needed to maintain the correct level.
- Check the Air Filter: A clogged air filter restricts airflow to the engine, which can cause it to overheat. Clean or replace the air filter as needed.
- Ensure Proper Ventilation: Make sure the engine has adequate ventilation. Don’t operate it in a confined space or near obstructions that can block airflow.
- Reduce Engine Load: Avoid overloading the engine by cutting thick grass in multiple passes or reducing the load on the engine.

Wood Processing Insights and Data

To put things in perspective, let’s consider some relevant data points and statistics related to wood processing and engine maintenance:

Fuel Efficiency: A well-maintained 675EX engine can consume approximately 0.75 to 1 gallon of gasoline per hour, depending on the load. Keeping the air filter clean and using fresh fuel can improve fuel efficiency by up to 15%.
Engine Lifespan: With proper maintenance, a 675EX engine can last for 500 to 1000 hours of use. Regular oil changes, air filter cleaning, and spark plug replacement are crucial for extending engine life.
Firewood Seasoning: Seasoning firewood reduces its moisture content, increasing its fuel value. Freshly cut wood can have a moisture content of 50% or higher, while seasoned wood should have a moisture content of 20% or less. Seasoning firewood for 6-12 months can increase its heat output by up to 50%.
Hardwood vs. Softwood: Hardwoods generally have a higher BTU (British Thermal Unit) rating than softwoods, meaning they produce more heat per unit volume. For example, oak has a BTU rating of around 28 million per cord, while pine has a BTU rating of around 20 million per cord.

Real-World Examples and Case Studies

Case Study 1: Reviving an Old Tiller: I once acquired an old garden tiller with a 675EX engine that had been sitting unused for several years. The engine was completely seized. After disassembling the engine, I found that the piston rings were rusted to the cylinder wall. I carefully cleaned the cylinder, replaced the piston rings, and reassembled the engine. With a new spark plug and fresh fuel, the engine started on the first pull and ran like new. This experience taught me the importance of proper engine storage and the potential for reviving seemingly hopeless engines.
Case Study 2: Optimizing Firewood Processing: I conducted a small-scale study to compare the efficiency of different firewood splitting methods. I found that using a hydraulic log splitter was significantly faster and less physically demanding than using a manual splitting maul. However, the manual maul provided a good workout and was more suitable for smaller logs. The key takeaway was that the best method depends on the size and quantity of wood being processed, as well as the individual’s physical capabilities.

Practical Tips and Actionable Advice

Preventative Maintenance: The best way to avoid engine problems is to perform regular preventative maintenance. This includes changing the oil, cleaning or replacing the air filter, replacing the spark plug, and using fresh fuel.
Proper Storage: When storing your engine for extended periods, drain the fuel tank and carburetor to prevent fuel degradation. Add fuel stabilizer to the fuel if you plan to store it for more than a few months. Store the engine in a clean, dry place.
Safety First: Always disconnect the spark plug wire before working on the engine to prevent accidental starting. Wear safety glasses and gloves when handling fuel and cleaning chemicals.
Document Your Work: Take pictures or videos as you disassemble the engine so you have a reference for reassembly. Label all parts and keep them organized.

Challenges Faced by Small Workshops and DIYers Globally

Limited Access to Tools and Parts: In some regions, access to specialized tools and replacement parts can be limited or expensive.
Lack of Training and Expertise: Many DIYers lack formal training in engine repair or wood processing techniques.
Budget Constraints: Small workshops and DIYers often operate on tight budgets, making it difficult to invest in expensive equipment or repairs.
Environmental Concerns: Sustainable wood processing practices and responsible engine maintenance are important considerations for DIYers who want to minimize their environmental impact.

Key Takeaways and Next Steps

Troubleshooting a Briggs & Stratton 675EX engine can seem daunting, but with a systematic approach and a little patience, you can often diagnose and fix the problem yourself. Remember to start with the simplest solutions first, such as replacing the fuel or spark plug, before moving on to more complex repairs. Regular maintenance is key to preventing engine problems and extending the life of your equipment.

Next Steps:

Identify the Symptoms: Carefully observe your engine’s behavior to identify the specific symptoms you’re experiencing.
Gather Your Tools and Supplies: Make sure you have the necessary tools and supplies for the repairs you plan to perform.
Follow the Troubleshooting Steps: Use the troubleshooting steps outlined in this article to diagnose the problem.
Perform the Repairs: Carefully perform the repairs, following the instructions and safety precautions.
Test Your Work: After completing the repairs, test the engine to make sure it is running properly.

By following these steps, you can keep your Briggs & Stratton 675EX engine running smoothly for years to come. And who knows, you might even discover a newfound passion for tinkering with small engines, just like I did!