Engine warning light on ('check engine') on a Kawasaki Ninja 650 2026

Faulty spark plug or ignition coil

The spark plug turns the high voltage supplied by the coil (5,000 to 30,000V depending on the system) into a spark between its two electrodes at the precise moment needed to ignite the compressed mixture. When it's fouled (a dry, black carbon deposit from poor carburetion or a 2-stroke engine), flooded (wet with fuel after several failed start attempts), worn (a rounded electrode after several thousand sparks), or damaged (a cracked white ceramic insulator), the spark becomes weak, erratic, or absent altogether. The gap between the electrodes needs to be set to the manufacturer's value -- generally 0.6 to 1.1mm depending on the model, always check the service manual or the sticker under the seat. Too small a gap gives a pale spark; too large a gap demands more voltage than the coil can always deliver. The standard torque is around 1.4 m.daN for a flat-seat plug with a gasket (NGK): hand-tighten until the gasket touches, then a quarter turn with the wrench. Overtightening strips the threads in the cylinder head -- an expensive repair. A standard plug lasts 10,000 to 20,000 km on average on a 4-stroke, less on a 2-stroke. An iridium or platinum plug lasts 30,000 to 40,000 km. Indicative cost: 4 to 15 euros each depending on type. Difficulty: Intermediate, a few simple tools are enough. Sources: NGK France, Le Repaire des Motards.

How to make the repair yourself

🟡 Intermediate level: a few basic tools and a bit of method are all you need. Work with a cold engine, take your time, and don't hesitate to stop the moment you're unsure.

1. 1Work with a cold engine (the cylinder head should be at room temperature: wait at least 30 minutes after shutdown). Locate the plug: on most single-cylinder bikes it's right in line with the cylinder; on V-twins there's one per cylinder; on inline four-cylinders, you'll need to remove the fuel tank to reach them.
2. 2Blow out or carefully brush away any debris around the plug well: even a speck of dust falling into the cylinder can cause damage. Pull off the spark plug cap (the rubber boot) by pulling straight, without twisting.
3. 3Unscrew the plug with a spark plug wrench of the correct size (often 16, 18, 20, or 21mm -- check yours to avoid slipping). Turn counterclockwise, and don't force it if it resists: a shot of penetrating fluid can help on a plug that's been in place for 20,000 km.
4. 4Examine the removed plug: light tan electrode = ideal, mixture is good; dry black = too rich or a dirty air filter; wet black = flooded with fuel; white = too lean, watch for overheating; cracked insulator = needs replacing.
5. 5If it's simply flooded, dry it completely (clean cloth, compressed air), clean the electrode with a brass brush, and reinstall. If it's fouled but mechanically sound, brass-brush it and reinstall. If wear is advanced or the insulator is damaged, replace it with the same reference (stamped on the plug: BPR7HS, CR8E, etc.).
6. 6Before installing a new plug, check the electrode gap with a feeler gauge: the exact value is in the manual or on the new plug's box. If needed, gently bend the side electrode (never the center one) to adjust it.
7. 7Thread the plug in by hand until the gasket touches the head, then tighten with the spark plug wrench about a quarter turn. If you have a torque wrench, aim for 1.4 m.daN (14 N.m) for the standard spec. Never force it -- you'll strip the head's threads.
8. 8Push the spark plug cap back on straight until it clicks into place. Start the engine: it should fire on the first or second try. If it still won't start, the plug wasn't the cause -- go back to the diagnosis.