RedMax EBZ8560 & EBZ8500 (Spark Plug Gap Specs)
For the RedMax EBZ8500 and EBZ8560, the specified spark plug is an NGK CMR7H, and its electrode gap is 0.6 mm (0.024 in). Check your exact model’s operator’s manual before servicing, since production or market revisions may differ. Work on a cool engine, measure with a wire gauge, and replace a damaged plug rather than trying to repair it.
A backpack blower that cranks but will not catch can turn a quick yard job into a frustrating diagnosis. The spark plug gap is one simple check, but it is not the only cause of a hard start or misfire. Here is how I check the plug on these models, set the gap carefully, and decide when the problem calls for more than a plug adjustment.
Equipment identification and specified plug
This section identifies the plug and gap to check on these two backpack blowers. Both are 65.6 cc, air-cooled, two-cycle machines. The listed plug is an NGK CMR7H, with an electrode gap of 0.6 mm (0.024 in). Confirm the model and manual before you begin, especially if the machine has a different label or service history.
| Blower model | Engine displacement | Specified spark plug | Electrode gap |
|---|---|---|---|
| RedMax EBZ8500 | 65.6 cc | NGK CMR7H | 0.6 mm (0.024 in) |
| RedMax EBZ8560 | 65.6 cc | NGK CMR7H | 0.6 mm (0.024 in) |
The gap is the space between the plug’s center and ground electrodes. It affects how far the spark must jump. Too wide a gap can make ignition less reliable; a plug with the wrong type or a damaged insulator can also cause trouble.
Check the identification label on the blower and use the operator’s manual that matches it. If the manual specifies a different part or gap for your exact serial number, market, or production version, follow that manual. Do not pick a plug based only on its appearance or assume a similar RedMax model uses the same part.
Key check: For the listed EBZ8500 and EBZ8560 specification, use CMR7H and 0.6 mm (0.024 in), subject to confirmation in the correct manual.
Safety and preparation before checking the gap
Preparation helps prevent burns, accidental starting, and damage to the plug threads. Do the work outdoors with the blower switched off and cool. Wear eye and hearing protection when operating the blower, and keep the test area clear before starting it. A clean work area also makes it less likely that debris will fall into the cylinder.
Before removing the plug:
- Set the ignition switch to OFF and let the engine cool.
- Place the blower on a stable surface outdoors.
- Disconnect the spark-plug cap by pulling on the cap, not the wire.
- Brush or wipe debris away from the plug and its surrounding area.
- Use the correct spark-plug tool so the plug can be removed straight.
Keep fuel and ignition sources apart, and do not smoke near the blower. Do not check for spark beside spilled fuel or while fuel vapors may be present. If the plug area is wet with fuel, stop and allow the area to air out before continuing.
Next step: Once the area is clean and the engine is cool, remove the plug and inspect it before adjusting anything.
Inspecting and setting the CMR7H spark-plug gap
A wire-type feeler gauge measures the space between the electrodes. For the specified setting, the correct wire should pass through the gap with light contact, not force. Adjust only the ground electrode, and avoid pressing on the center electrode or ceramic insulator. If either part is damaged, replace the plug.
- Remove the plug with the correct tool, turning it counterclockwise. Keep the tool aligned with the plug.
- Look over the ceramic insulator and both electrodes. Replace the plug if the ceramic is cracked, an electrode is damaged, or deposits are heavy and will not clean away.
- Select the 0.6 mm (0.024 in) wire on a wire-type feeler gauge. Slide it between the electrodes without forcing it.
- If adjustment is needed, bend the ground electrode in small steps. Recheck the gap after each change.
- Stop if the electrode is loose, distorted, or cannot be set reliably. Fit a new, verified plug instead.
A flat gauge can be harder to use on some electrode shapes. Do not wedge a gauge into the gap or use it as a lever. Excess force can change the gap or damage the center electrode. If you are unsure whether the gauge reading is correct, compare it with the manual’s method or ask a qualified service shop.
| What you find | Recommended response |
|---|---|
| Gap measures 0.6 mm (0.024 in), plug is sound | Reinstall the plug |
| Gap is off, electrodes and insulator are sound | Adjust the ground electrode gently, then recheck |
| Cracked insulator, damaged electrodes, or persistent heavy fouling | Replace with the specified plug |
| Plug type or manual is uncertain | Confirm the exact model and manual before fitting a plug |
Key takeaway: Measure rather than guess. A plug that is cracked or badly worn is not a good candidate for adjustment.
Reinstalling the plug and checking the blower
Correct installation protects the cylinder-head threads and gives the plug a sound seat. Start the plug by hand, with the blower cool and the cap disconnected. Tightening details can vary, so use the torque or installation instructions in the manual for your exact unit. Never force a plug that does not turn smoothly.
Thread the plug in by hand first. If it resists, back it out and check that it is aligned; forcing it can cross-thread the plug and damage the cylinder head. Once it is seated by hand, tighten it as directed in the manual. Do not guess at a torque value or use excessive force.
Reconnect the plug cap securely after installation. Move the blower outdoors to a clear area, follow the normal starting procedure in the manual, and make a brief test. Stop if the engine misfires, will not run normally, or the plug seems loose or improperly seated. Switch off and investigate instead of continuing to run the blower.
The plug gap is one part of ignition condition, not a complete diagnosis. If the gap is correct and the plug is sound but the blower still starts poorly, check the model manual for other approved checks, such as fuel condition and air-filter service. Do not assume that changing the gap will solve a problem caused elsewhere.
Next step: If the plug seats correctly and the blower runs steadily, record the service. If not, stop and troubleshoot with the manual or a qualified technician.
Fuel mix, seasonal service, and storage
Fuel quality and the correct oil mix matter to a two-cycle engine, but they do not change the required plug gap. The specified mix for these models is 50 parts gasoline to 1 part suitable air-cooled two-cycle oil. Use fresh fuel prepared to that ratio, and follow the manual for fuel handling, service intervals, and storage.
For a 50:1 mix, use the product’s marked measuring directions to combine gasoline and oil accurately. Do not run straight gasoline in a two-cycle engine. Do not use an oil type or fuel preparation method that conflicts with the operator’s manual.
Seasonal storage can leave old fuel in the system, and a fouled plug can be one sign of an engine that has not been running well. It is not proof of a particular fuel problem. Inspect the plug and follow the manual’s storage and maintenance steps rather than trying to diagnose the whole engine by plug color alone.
After service, switch the blower off and let it cool. Clean debris from the exterior and air-intake area without pushing dirt into openings. Record the date, plug condition, and any replacement made. Follow the manual’s inspection schedule rather than relying on a universal interval.
Key takeaway: Keep the plug setting, fuel ratio, and storage procedure separate in your notes. Each is a different maintenance check.
Common service scenarios and what to do
These examples show how I would approach common plug-related situations; they are troubleshooting scenarios, not reports of a particular repair. The aim is to use the gap specification as a measured check, then stop when the evidence points to damage or another fault.
Scenario: The blower is hard to start after storage. I would first confirm the model, inspect the plug, and measure the gap. If the CMR7H is sound and measures 0.6 mm (0.024 in), I would reinstall it according to the manual and check the manual’s fuel and storage steps. I would not widen the gap to make the engine “spark harder.”
Scenario: The plug gap is too wide. If the plug is otherwise in good condition, I would make a small adjustment to the ground electrode and measure again. If I could not set it accurately, or the electrode looked damaged, I would replace the plug with the specified type.
Scenario: The plug will not turn freely during installation. I would stop, remove it, and restart the threads by hand with the plug aligned. A plug that binds should not be forced with a wrench. If the threads appear damaged or the plug will not seat correctly, I would leave the engine off and seek qualified service.
| Symptom or finding | First action | Stop and get help when |
|---|---|---|
| Hard starting, plug appears sound | Confirm model, plug type, and measured gap | The blower still will not run normally after manual-approved checks |
| Misfire with a gap outside specification | Set to 0.6 mm (0.024 in) if the plug is undamaged | The plug is cracked, worn, or cannot be adjusted reliably |
| Plug binds while being installed | Remove it and restart by hand | It still binds or cylinder-head threads look damaged |
| Blower runs poorly after plug service | Switch off and recheck seating and cap connection | Misfire continues or safe operation is uncertain |
Takeaway: A correct gap does not excuse a damaged plug, poor seating, or an unresolved engine fault.
Frequently asked questions
What is the spark-plug gap for the EBZ8500 and EBZ8560?
The listed gap is 0.6 mm (0.024 in) with an NGK CMR7H spark plug. Confirm the correct manual for your exact machine before service.
Which spark plug is specified?
The listed plug is an NGK CMR7H. Do not substitute another plug unless the manual for your model and production version approves it.
Can I use a flat feeler gauge?
A wire-type feeler gauge is recommended for checking the electrode gap. Use the 0.6 mm (0.024 in) wire and do not force it between the electrodes.
Should I adjust the center electrode?
No. Make any small gap adjustment at the ground electrode. Avoid levering against the center electrode or ceramic insulator.
What if the spark plug is cracked?
Replace it with the specified plug after confirming the manual. Do not try to repair or reuse a plug with a cracked insulator.
Can an incorrect gap cause hard starting or misfiring?
It can contribute to ignition problems. A gap that is too wide may make ignition less reliable, but hard starting can have other causes too.
What fuel mix do these blowers use?
The specified ratio is 50:1 gasoline to suitable air-cooled two-cycle oil. Use fresh fuel and check the operator’s manual for fuel guidance.
How tight should I install the plug?
Use the installation or torque instructions in the manual for your exact model. Start the plug by hand, and never force it into the cylinder-head threads.
What should I do if the correct gap does not fix the problem?
Switch the blower off and follow the manual’s other troubleshooting checks. If misfiring or hard starting continues, have the machine inspected rather than running it with an unresolved fault.
Can I check the plug while the engine is hot?
No. Let the engine cool before removing the plug. This lowers burn risk and helps protect the plug and cylinder-head threads during service.
A careful plug check is straightforward: verify the model, use the specified CMR7H, measure 0.6 mm (0.024 in), and reinstall it by hand before tightening as directed. If the plug is damaged, binds, or the blower still runs poorly, stop and use the correct manual or qualified service support.
(This article was written by one of our staff writers, Harrison Croft. Visit our Meet the Team page.)
