Husqvarna 240 Spark Restoration (Troubleshooting)
A Husqvarna 240 that will not start needs a spark test before it needs parts. Work outdoors with the saw cool, isolate the plug, and check the plug, lead, stop circuit, and ignition-module gap in order. If spark returns but the engine still will not fire, move on to fuel, flooding, exhaust, and compression checks.
Thirty pulls without a start can turn a small fault into an expensive guessing game. The fastest way forward is to test one part of the ignition system at a time. I start with safety and the plug, then work toward wiring and the ignition module. That order helps avoid replacing a good module when a damaged lead or stop wire is the real cause.
A spark fault is only one cause of a no-start. A wet plug, old fuel, blocked exhaust, or low compression can produce similar symptoms. The checks below help separate those problems without assuming the saw needs a particular part.
Equipment Setup & Safety Prep
This stage makes the spark test safer and more useful. Confirm the saw is a Husqvarna 240, work outside on a cool machine, and keep fuel vapors away from any spark source. The 240 is a 38.2 cm³, two-stroke saw, but parts and service details can vary by model and market.
Wear eye protection and gloves. Engage the chain brake, set the stop switch to STOP, and remove the spark-plug boot before inspecting anything. Keep the saw away from flames, pilot lights, spilled fuel, and open fuel containers.
Gather the right tools
A basic check needs the correct replacement plug, a gap gauge, and an inline spark tester if available. A nonmagnetic feeler gauge or the specified service gauge is useful for setting the ignition-module air gap. Use the owner’s manual or parts listing for the exact plug type; a plug that fits the threads is not necessarily the right plug.
Do not test spark near the plug hole. Fuel vapor can escape there. An inline tester avoids removing the plug for the test and is the safer choice. If you use the plug itself, keep its metal shell firmly grounded to the cylinder and its electrode well away from the plug hole. Never crank with an ungrounded lead.
Field Cutting/Landscaping Operation
This is the core diagnostic sequence: inspect the plug, test for spark, and then isolate the likely fault. Change one thing at a time and retest. A visible spark does not prove the whole saw is healthy, but a repeatable no-spark result gives you a clear ignition problem to trace.
1. Inspect the plug
Remove the plug and look for cracks, heavy carbon, oil fouling, or damage. Replace it if it is cracked, heavily fouled, or not the specified type. Set the electrode gap to 0.5 mm (0.020 in), unless the manual for your exact saw specifies otherwise.
A wet plug may indicate flooding, especially after repeated start attempts. Dry or replace it, then follow the manual’s clearing and starting procedure. Do not keep pulling the starter with fuel vapor around the saw.
2. Test for spark
Reconnect the plug boot to an inline tester and crank the saw as directed by the tester instructions. If the tester shows no spark, check the boot and lead for cuts, looseness, corrosion, or contact with the flywheel. Also inspect visible wiring and connectors for damage.
If you test with the plug, ground its metal shell securely to the cylinder. Keep the plug and spark away from the plug opening and any fuel. A weak or intermittent result deserves the same careful inspection as no spark.
3. Check the stop circuit
The stop switch shuts the engine off by grounding the ignition circuit. A damaged, rubbed-through, loose, or pinched stop wire can keep the system grounded and prevent spark. Inspect the switch and wiring for damage or poor connections.
Do not run the saw with the stop circuit bypassed. A qualified technician may isolate the circuit as a controlled diagnostic test, but the wiring must be restored and the stop function tested before the saw is started for use. If the switch cannot reliably stop the engine, do not operate the saw.
4. Inspect the module and air gap
If the plug, lead, and stop circuit check out, inspect the ignition module and flywheel area. Look for damage, a loose module, or signs that the flywheel has contacted the lead or module. Check the module air gap and set it to 0.3 mm (0.012 in) using the specified gauge or a nonmagnetic feeler gauge.
Do not file or bend ignition parts to make them work. If wiring is damaged, repair or replace it correctly. If the module fails testing or is visibly damaged, replace it with the correct part for the saw’s exact variant.
Quick results table
| Test result | Most useful next check | Avoid |
|---|---|---|
| Plug is cracked or heavily fouled | Fit the correct plug; set gap to 0.5 mm | Choosing a plug by appearance alone |
| Plug is wet after repeated pulls | Clear flooding per the manual; retest | Continuing to crank beside fuel vapor |
| Inline tester shows no spark | Inspect boot, lead, stop wire, and connectors | Replacing the module before checking wiring |
| Spark is intermittent | Check loose connections, rubbed wire, flywheel, and module gap | Filing or bending ignition parts |
| Spark is present but saw will not start | Check fuel condition, air filter, exhaust, and compression | Assuming ignition is the only fault |
Two common diagnostic patterns
One common pattern is a saw that shows no spark until a damaged stop wire is found near the handle or housing. The module may be sound; the wire is grounding the ignition circuit. Repairing the damaged wiring and confirming the stop switch works can resolve that specific fault.
Another pattern is a wet plug and no start after many pulls. That points first toward flooding, not automatically toward a failed module. Dry or replace the plug, follow the manual’s clearing procedure, then retest. These are diagnostic examples, not proof of what is wrong with your saw.
5. Restart and verify
Once spark is restored, reinstall the plug and boot, confirm the stop switch is connected, and use the manual’s cold- or warm-start procedure. If the engine still will not start, stop treating it as an ignition-only problem. Check fresh fuel mixed at 50:1 with suitable two-stroke oil: 20 mL of oil per 1 L of gasoline. Follow the oil maker’s instructions and use fresh fuel.
Then inspect the air filter and exhaust or spark-arrestor screen for obstruction. If the fault remains, compression may need testing with the correct gauge and service procedure. Do not change carburetor settings to compensate for absent or weak spark.
Maintenance & Sharpening/Tuning
Routine checks can catch ignition faults before the next job. Keep the correct plug clean and gapped, and inspect the boot, lead, and stop wire during service. Confirm replacement parts against the exact model or serial information rather than relying on the “240” name alone.
Published 240 references commonly give 3,000 rpm idle and 9,000 rpm maximum, but service data can vary by model or market. Use the applicable manual and a tachometer for adjustment; do not tune by ear or exceed the specified speed. Do not adjust the carburetor while diagnosing a spark fault.
Before cutting, check that the chain is properly tensioned, sharp, and lubricated, and that the brake works. Bar length, chain gauge, and drive-link count vary by setup. Match the chain to the bar and sprocket markings rather than ordering by model name alone.
Storage & Seasonal Care
Storage affects the next start as well as ignition reliability. Follow the owner’s manual for fuel-system storage and return-to-service steps. Keep the saw cool, dry, and clean, and protect ignition parts from corrosion and fuel or oil contamination.
When bringing the saw back into use, inspect the lead, boot, plug, and stop switch before starting. Use fresh, correctly mixed fuel. After any ignition repair, test that the stop switch shuts the engine off; do not cut if it fails.
Conclusion
Work from the plug outward: check the plug, test spark, inspect the lead and stop circuit, then verify the module gap. If spark is back but the saw remains dead, check fuel, flooding, intake, exhaust, and compression instead of buying ignition parts at random. Restore and test the stop switch before returning the saw to service.
FAQ
What spark-plug gap does a Husqvarna 240 use?
The stated gap is 0.5 mm (0.020 in). Confirm the plug type and gap against the manual for your exact saw.
What is the ignition-module air gap?
The stated module air gap is 0.3 mm (0.012 in). Use the specified gauge or a nonmagnetic feeler gauge.
Can I test the saw’s spark by holding the plug against the cylinder?
Only if the plug’s metal shell is firmly grounded and the electrode is kept well away from the plug hole and fuel. An inline tester is preferable.
What does a wet spark plug mean?
It can indicate flooding after repeated starting attempts. Follow the manual’s clearing procedure, then retest. A wet plug alone does not prove the carburetor or ignition module has failed.
Why is there no spark even with a new plug?
Check the plug boot, lead, connectors, stop switch, and stop wire before suspecting the module. A wire grounding the ignition circuit can prevent spark.
Can I run the saw with the stop wire disconnected?
No. The stop switch may not shut the engine off. Restore the circuit and verify the switch works before starting the saw for use.
What fuel mix should I use?
The stated mix is 50:1, or 20 mL of suitable two-stroke oil per 1 L of gasoline. Follow the oil maker’s instructions and the saw manual.
The tester shows spark, but the saw still will not start. What next?
Check for flooding, stale or incorrect fuel, a blocked air filter or exhaust, and low compression. Spark does not rule out other faults.
Should I adjust the carburetor to fix a weak spark?
No. Carburetor adjustments do not repair an ignition fault. Diagnose the ignition system first, and use the correct service data for any later tuning.
What should I verify before cutting after an ignition repair?
Confirm the stop switch shuts the engine off, the chain brake works, the chain is correctly matched to the bar and sprocket, and the saw idles without the chain moving.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
