How To Test A Briggs And Stratton Coil

Okay, let me tell you a little story. Last summer, my neighbor, bless his heart, was wrestling with his lawnmower. It was sputtering, backfiring, the whole nine yards. He spent a week convinced it was the carburetor, cleaning it, rebuilding it, the whole shebang. Turns out? A simple, silly coil. Go figure! That got me thinking – how many people are out there chasing ghosts when a simple coil test could save them hours of frustration? (Probably a lot, right?). That's why we're here today: to demystify the process and get your Briggs & Stratton engine purring again.

Why Test Your Coil?

Before we dive into the how-to, let's quickly cover the why. Your Briggs & Stratton engine coil, also known as the ignition coil, is basically the heart of your engine's ignition system. It takes the low voltage from the battery (or sometimes directly from the flywheel) and amplifies it into a high-voltage spark that ignites the air-fuel mixture in the cylinder. No spark, no boom, no running engine. Simple as that.

So, if your engine is:

• Not starting (the classic symptom)
• Starting hard
• Running rough
• Misfiring (like it's hiccuping)
• Lacking power

... then your coil is a prime suspect. But don't just go throwing parts at it! Let's do some detective work first. Save yourself some money (and the inevitable frustration of replacing something that wasn't broken in the first place!).

Safety First! (Duh)

Before we even think about touching anything, let's talk safety. We're dealing with electricity here, albeit relatively low voltage (usually). But still, treat it with respect. And remember, we are working around gasoline, which is flammable, so no smoking!

Here's a quick checklist:

• Disconnect the spark plug wire: Always, always, always disconnect the spark plug wire from the spark plug before working on the ignition system. Tuck it safely away from the plug to prevent accidental sparking.
• Wear safety glasses: Because flying debris is never a good look.
• Work in a well-ventilated area: Fumes are bad, m'kay?
• Disconnect the battery (if applicable): Some engines have batteries, some don't. If yours does, disconnect the negative terminal.

Okay, safety briefing over. Let's get our hands dirty!

Tools You'll Need

Luckily, you don't need a whole garage full of fancy equipment for this. Here's what you'll likely need:

• A multimeter: This is your best friend for electrical testing. You'll need one that can measure resistance (Ohms) and sometimes voltage. A basic digital multimeter will do just fine. (Don't be scared of it! We'll walk you through it.)
• An ohmmeter (Most multimeters have this feature)
• A spark plug tester: A simple, inexpensive tool that visually confirms if the coil is producing a spark. A great quick check.
• A feeler gauge: For setting the air gap (more on that later).
• A screwdriver (various sizes): For removing the engine cover and coil.
• A socket set: Depending on the engine, you might need sockets to remove the coil.
• A wire brush or sandpaper: For cleaning the coil and flywheel surfaces. Clean surfaces are happy surfaces.
• Your engine's repair manual (optional but highly recommended): It'll have the specific resistance values for your coil.

Testing Method 1: The Spark Plug Tester (The Quick & Dirty Method)

This is the easiest way to get a quick sense of whether your coil is working at all. It's not definitive, but it's a good starting point. It won't tell you how well it's working, but it will tell you if it's working.

1. Connect the spark plug tester: Remove the spark plug (after disconnecting the spark plug wire, remember!) and screw the tester into the spark plug hole. Then, attach the spark plug wire to the tester.
2. Ground the tester: The tester needs to be grounded to the engine. Most testers have a clip or wire for this purpose. Make sure it's securely connected to a clean, unpainted metal surface on the engine.
3. Crank the engine: Pull the starter rope (or turn the key, if it's a battery-start engine) and watch the tester.
4. Look for a spark: If you see a bright, consistent spark jumping across the gap in the tester, your coil is likely producing enough voltage to ignite the fuel. (Hooray!) If you see no spark, a weak spark, or an intermittent spark, your coil is suspect.

Side note: If you're getting a spark, but the engine still won't start, the problem is likely elsewhere (fuel, compression, timing, etc.). This is where a good troubleshooting process comes in handy!

Testing Method 2: The Multimeter Test (For the More Adventurous)

This method is more precise and involves using a multimeter to measure the resistance of the coil's windings. You'll need to know the expected resistance values for your specific coil, which you can usually find in your engine's repair manual or online.

There are two key resistance measurements we'll be taking:

• Primary Resistance: This is the resistance of the primary winding, which is the low-voltage side of the coil.
• Secondary Resistance: This is the resistance of the secondary winding, which is the high-voltage side of the coil.

Step 1: Accessing the Coil

1. Remove the engine cover: You'll need to remove the engine cover to access the coil. The cover is usually held in place by screws or bolts.
2. Locate the coil: The coil is usually mounted near the flywheel, close to the spark plug. It's a small, rectangular component with a wire leading to the spark plug.
3. Disconnect the coil wires: Disconnect any wires connected to the coil. Make sure to note where they go, so you can reconnect them correctly later.

Step 2: Measuring Primary Resistance

1. Set the multimeter to the Ohms (Ω) setting: Start with a low range, such as 200 Ohms.
2. Connect the multimeter probes: Connect one probe to the coil's primary terminal (usually the terminal where the low-voltage wire was connected) and the other probe to the coil's metal core or mounting bracket (which should be grounded).
3. Read the resistance: Observe the reading on the multimeter. It should be within the range specified in your engine's repair manual. A typical value for primary resistance is between 0.5 and 5 Ohms, but always check your manual.
4. Interpreting the results:
   • If the reading is within the specified range: The primary winding is likely good.
   • If the reading is zero or close to zero: There's a short circuit in the primary winding. The coil is bad.
   • If the reading is infinite or very high: There's an open circuit in the primary winding. The coil is bad.

Step 3: Measuring Secondary Resistance

1. Keep the multimeter set to the Ohms (Ω) setting: You might need to increase the range to measure higher resistances. Try 20k Ohms.
2. Connect the multimeter probes: Connect one probe to the coil's spark plug terminal (where the spark plug wire connects) and the other probe to the coil's metal core or mounting bracket (again, grounded).
3. Read the resistance: Observe the reading on the multimeter. Again, it should be within the range specified in your engine's repair manual. A typical value for secondary resistance is between 3,000 and 15,000 Ohms, but seriously, check your manual.
4. Interpreting the results:
   • If the reading is within the specified range: The secondary winding is likely good.
   • If the reading is zero or close to zero: There's a short circuit in the secondary winding. The coil is bad.
   • If the reading is infinite or very high: There's an open circuit in the secondary winding. The coil is bad.

The Air Gap: A Crucial Detail

Even if your coil passes the resistance tests, it still might not be working correctly if the air gap between the coil and the flywheel is incorrect. The air gap is the small space between the coil's armature (the metal part that sits near the flywheel) and the flywheel itself.

The correct air gap is crucial for the coil to generate enough voltage. If the gap is too wide, the spark will be weak or nonexistent. If the gap is too narrow, the coil can overheat and be damaged.

Here's how to check and set the air gap:

1. Locate the air gap: The air gap is the space between the coil's armature and the flywheel.
2. Use a feeler gauge: Insert the feeler gauge with the correct thickness (usually 0.010" or 0.012", but check your manual!) between the coil's armature and the flywheel's magnets.
3. Loosen the coil mounting bolts: Loosen the bolts that hold the coil in place just enough so that you can move the coil slightly.
4. Position the coil: With the feeler gauge in place, gently push the coil against the flywheel until it makes contact with the feeler gauge.
5. Tighten the coil mounting bolts: Tighten the bolts while holding the coil in position. Be careful not to overtighten them.
6. Remove the feeler gauge: Remove the feeler gauge. The air gap should now be correctly set.

Cleaning the Surfaces

While you're at it, take a moment to clean the surfaces of both the coil's armature and the flywheel where they make contact. Use a wire brush or sandpaper to remove any rust, corrosion, or dirt. A clean surface ensures a good electrical connection.

Reassembly and Testing

Okay, you've tested the coil, checked the air gap, and cleaned the surfaces. Now it's time to put everything back together.

1. Reinstall the coil: Carefully reinstall the coil, making sure the air gap is still correct.
2. Reconnect the coil wires: Reconnect any wires you disconnected from the coil, making sure they're connected to the correct terminals.
3. Reinstall the engine cover: Reinstall the engine cover.
4. Reconnect the spark plug wire: Reconnect the spark plug wire to the spark plug.
5. Test the engine: Try starting the engine. If everything is working correctly, it should start easily and run smoothly.

Still No Spark? What Now?

If you've followed all these steps and you're still not getting a spark, it's possible that the coil is indeed bad. However, before you run out and buy a new coil, there are a few other things you should check:

• Check the flywheel key: The flywheel key is a small key that connects the flywheel to the crankshaft. If the key is sheared or damaged, the timing will be off, and the engine won't start.
• Check the kill switch: The kill switch is a switch that grounds the ignition system, preventing the engine from starting. Make sure the kill switch is in the "run" position. Sometimes the wire can be frayed and cause issues with starting.
• Check the wiring: Inspect all the wiring in the ignition system for any damage, corrosion, or loose connections.
• Consider the CDI module (if applicable): Some Briggs & Stratton engines use a Capacitive Discharge Ignition (CDI) module. This module stores electrical energy and discharges it to the coil. If the CDI module is faulty, it can prevent the coil from generating a spark.

Replacing the Coil (The Last Resort)

If you've exhausted all other possibilities and you're still convinced the coil is bad, it's time to replace it. Fortunately, replacing a coil is usually a straightforward process.

1. Purchase a new coil: Make sure you get the correct coil for your specific engine model. You can usually find this information in your engine's repair manual or online.
2. Remove the old coil: Follow the steps outlined above for accessing the coil.
3. Install the new coil: Install the new coil, making sure the air gap is correctly set.
4. Reconnect the coil wires: Reconnect any wires you disconnected from the old coil.
5. Reinstall the engine cover: Reinstall the engine cover.
6. Reconnect the spark plug wire: Reconnect the spark plug wire to the spark plug.
7. Test the engine: Try starting the engine. If everything is working correctly, it should start easily and run smoothly.

Final Thoughts

Testing a Briggs & Stratton coil might seem intimidating at first, but it's actually a fairly simple process. By following these steps, you can diagnose ignition problems, save money on unnecessary repairs, and get your engine running smoothly again. And hey, even if you do end up needing to replace the coil, at least you'll know you did your due diligence! Now go forth and conquer those stubborn engines!