28d • General discussion
Spark plugs are one of the simplest and most overlooked diagnostic.
Beyond firing the spark, a plug tells a story about what’s happening inside the engine. The colour and condition of the electrode and insulator can point to mixture, combustion quality, and operating conditions.
A plug that’s light tan or gray typically indicates normal combustion. Dark, wet, or sooty plugs often point to rich operation, excessive idling, short run times, or cold-weather use where the engine never fully warms up. This is common on sleds and small engines that see lots of starts and stops.
Plugs that look unusually white, blistered, or worn can indicate higher operating temperatures, lean conditions, or excessive load. That’s not something to ignore, especially on two-stroke engines where lubrication depends on proper mixture.
Correct plug heat range matters. A plug that’s too cold may never burn off deposits and will foul easily. A plug that’s too hot can overheat and cause pre-ignition. Using the manufacturer’s recommended plug is usually the safest baseline unless other modifications are in place.
The gap also matters more than people realize. A gap that’s too wide can cause a weak spark under load, while a gap that’s too tight can reduce combustion efficiency. Checking and setting the gap during routine maintenance helps keep starting and throttle response consistent.
Spark plugs aren’t just parts you replace when something goes wrong. They’re one of the easiest ways to check engine health before problems show up.
When was the last time you actually looked at the plug you pulled out?
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Spark plugs are one of the simplest and most overlooked diagnostic.
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