Husqvarna 350 Ignition & Spark Problems (Spark Test)
If your Husqvarna 350 will not start, test ignition before buying a coil. Use a commercial spark tester, keep sparks far from fuel and vapors, and check the plug, lead, stop-switch circuit, and ignition module in order. A steady tester indication means spark is present, but it does not prove the saw will run.
Repeated pulls can leave you with a sore arm and no clear answer. The key is to separate an ignition fault from a fuel or compression problem before replacing parts. On a Husqvarna 350, start with the spark plug and a safe spark test, then follow the result one step at a time.
The common 350 versions have a 49.4 cm³, air-cooled two-stroke engine. Details can vary by year and version, so check the manual for your specific saw before ordering parts or adjusting the ignition module. A correct test now can prevent an unnecessary coil purchase.
Equipment Setup and Safety Preparation
A safe setup keeps fuel vapor away from any test spark and makes the result easier to trust. Work outdoors, away from flames, heaters, cigarettes, and other ignition sources. Wear eye and hand protection, engage the chain brake, switch the saw off, and let a hot engine cool before removing the plug.
A spark can ignite vapor even when you cannot see or smell a dangerous amount of fuel. Never test beside an open spark-plug hole or a fuel-soaked saw. If fuel has spilled, stop and let it evaporate fully in a well-ventilated area before you continue.
Before testing:
- Set the saw on firm ground and clear loose debris.
- Check that the chain brake is engaged and the bar is clear.
- Look over the plug boot, lead, stop-switch wiring, and visible module wiring for cracks, cuts, loose connections, or signs of rubbing.
- Keep fuel containers away from the work area.
- Use a commercial spark tester and follow its instructions.
The stop switch grounds the ignition circuit to stop the engine. Damaged or pinched wiring can keep the circuit grounded and prevent spark. Do not leave this circuit disconnected after testing. A working stop switch is essential before the saw goes back into use.
How to Test Spark on a Husqvarna 350
A spark test checks whether the ignition system can produce a visible electrical discharge at the plug or tester. Use a commercial inline tester connected between the plug lead and spark plug, or a grounded tester used exactly as its maker directs. Do not hold a loose plug near the cylinder to look for spark.
First, remove the plug boot and unscrew the plug. Check the plug for fuel wetness, heavy carbon, cracks, or a damaged electrode. A fouled or incorrect plug can confuse the diagnosis. Common 350 versions specify a Champion RCJ7Y plug with a 0.5 mm (0.020 in) electrode gap, but confirm the plug type in the manual for your saw’s year and version.
Install the tester as directed. Keep it and any exposed spark well away from the plug hole, spilled fuel, and fuel containers. Pull the starter and watch the tester. A consistent indication means the ignition is producing spark at the test point. No indication means continue with the isolation steps below.
| Test result | What it tells you | Next step |
|---|---|---|
| No tester indication | Spark is not reaching the tester, or the setup is faulty | Check connections, then retest with a known-good specified plug |
| Consistent indication | Spark is present at the test point | Refit the plug and investigate fuel or compression if the saw still will not start |
| Spark appears only when wiring is moved | A loose or damaged connection may be present | Inspect the lead, boot, and module wiring |
| Tester result changes between pulls | The fault may be intermittent, or the tester connection may be loose | Secure the connections and repeat the test safely |
Do not judge the ignition only by the color of a spark. A visual spark in open air does not prove the system will work under engine conditions. Likewise, a failed result can come from a poor tester connection, so check the setup before condemning a part.
Isolate the Plug, Stop Circuit, and Ignition Module
Isolation means changing or checking one part at a time so the test points toward the cause. On a no-spark Husqvarna 350, work from the simple items toward the ignition module. Confirm each connection before moving on; replacing parts without a test can waste money and leave the real fault in place.
1. Retest with a known-good plug
Fit a known-good plug of the specified type and set the gap to 0.5 mm (0.020 in), if that is the value listed for your version. Retest with the same commercial tester setup. If spark returns, the original plug was likely the problem. If not, continue.
A plug that looks acceptable may still fail in use. The tester helps separate a plug fault from a problem farther back in the ignition circuit.
2. Inspect the boot and lead
Check that the boot grips the plug terminal and that the ignition lead is fully attached. Look for cuts, crushed spots, loose ends, or contact with sharp or hot parts. Do not pull hard on the wire; inspect and handle the boot itself. Repair or replace damaged parts only with compatible components.
3. Check the stop-switch circuit
The stop-switch wire can short to ground if it is pinched, worn, or incorrectly routed. Inspect the wire and switch for visible damage and loose connections.
If the wiring appears sound but the saw still has no spark, a controlled diagnostic test may involve disconnecting the stop-switch lead at the ignition module, then repeating the spark test. Do this only if you can identify the correct lead and follow the service manual. If spark returns, the switch or its wiring is likely grounding the circuit. Reconnect the lead as soon as the test is done. Never operate the saw with the stop circuit disconnected.
4. Inspect the module and air gap
If there is still no spark, inspect the module connections and mounting for damage or looseness. The air gap is the space between the ignition module and the flywheel. Common 350 service specifications are approximately 0.3 mm (0.012 in), but verify the correct manual before adjusting it. Do not guess at the gap or force the module against the flywheel.
If the gap and wiring are correct and a known-good plug still gives no spark, a failed ignition module becomes more likely. Confirm the tester, connections, and stop-circuit test before replacing it. A module should be replaced based on the test sequence, not simply because the saw will not start.
What to Check After a Spark Test
A spark indication rules out a complete loss of spark at the tester, but it does not confirm fuel delivery, compression, or correct ignition timing. If the saw still will not start, refit the plug and boot, restore all wiring, then move to fuel and compression checks rather than replacing ignition parts without evidence.
A wet plug after repeated starting attempts can mean the cylinder is receiving fuel, but it may also be flooded. A dry plug can point toward a fuel-delivery issue. Neither clue proves the cause by itself. Follow the model’s starting procedure and avoid adding fuel directly into the cylinder unless the service instructions specifically call for it.
Use the fuel specified for the saw. Common 350 versions use a 50:1 (2%) mix of gasoline and quality air-cooled two-stroke oil. Do not use straight gasoline. Incorrect or stale fuel can cause starting trouble even when the spark test passes.
Two common diagnostic patterns illustrate why the order matters:
- Example: spark returns with a replacement plug. The test points first to a fouled or failed plug, not automatically to the module. Confirm the specified plug and gap, then test the saw using the normal starting method.
- Example: spark returns only during a controlled stop-wire test. The result points toward a stop switch or wiring fault. Repair that circuit and confirm the stop switch shuts the engine off before running the saw.
These are diagnostic examples, not proof that every 350 has the same fault. If your results do not match either pattern, record what changed between tests and consult the correct service information.
Before starting the saw, refit the plug and boot, reconnect the stop circuit, and verify that the stop switch works. Start only on firm ground, with the chain brake engaged and the bar clear. Do not cut until the chain brake, throttle lockout, and chain lubrication are working correctly.
Frequently Asked Questions
What spark plug does a Husqvarna 350 use?
Common versions specify a Champion RCJ7Y, with a 0.5 mm (0.020 in) electrode gap. Check the manual for your exact model version before fitting a plug.
How do I test spark on a Husqvarna 350?
Use a commercial inline spark tester between the plug lead and plug, following the tester instructions. Keep it far from the plug hole and all fuel or vapor.
Can I hold the spark plug against the cylinder to test it?
Do not use that method near an open plug hole or fuel vapor. Use a commercial tester to reduce the risk of igniting fuel.
What does no spark usually mean?
It means spark is not reaching the test point, or the test connection is faulty. Check the tester setup, try a known-good specified plug, then inspect the lead, stop circuit, and module.
Could a bad stop switch prevent spark?
Yes. A shorted stop-switch wire can ground the ignition circuit and prevent spark. Repair the fault and reconnect the circuit before operating the saw.
What air gap should the ignition module have?
Common 350 service specifications are about 0.3 mm (0.012 in). Verify the value in the service manual for your saw before adjusting it.
Does visible spark mean the ignition system is good?
No. A spark at the tester shows output at that test point, but it does not prove the saw will run or that fuel and compression are correct.
Why does the saw still not start when spark is present?
Check for a fouled plug, flooding, incorrect or stale fuel, fuel-delivery problems, or low compression. A spark test checks ignition output only.
Can I start the saw with the stop-switch wire disconnected?
No. Reconnect it after any controlled diagnostic test and verify that the stop switch shuts the engine off before use.
What fuel mix does the Husqvarna 350 use?
Common versions specify 50:1 (2%) gasoline and quality air-cooled two-stroke oil. Check your manual and never run the saw on straight gasoline.
(This article was written by one of our staff writers, Robert Callahan. Visit our Meet the Team page.)
