What are the symptoms of a faulty motorcycle spark plug?

[LeIvan]

Motorcycle spark plug failure symptoms requiring replacement: difficulty starting, low power, excessive exhaust emissions, increased fuel consumption; severe spark plug damage with phenomena such as blistering at the top, black streaks, cracking, or electrode melting. Methods to determine if a spark plug is damaged: Remove the spark plug for observation and assess its condition based on the following appearance colors. A normal spark plug's insulator skirt and electrodes appear gray-white, gray-yellow, or light brown. A properly functioning spark plug has a reddish-brown insulator skirt, with an electrode gap between 0.8-0.9mm and no signs of electrode burn. If the spark plug is contaminated with oil or deposits but is not damaged, it can continue to be used after cleaning off the oil and deposits. If the spark plug is severely damaged, showing blistering at the top, black streaks, cracking, electrode melting, etc., the cause of the damage should be identified. After troubleshooting, replace the spark plug with a new one. Additionally, if the spark plug appears black as if smoked, it indicates the wrong heat range was selected or the air-fuel mixture is too rich, with oil seepage.

[Millard]

I previously encountered a spark plug issue while riding my motorcycle, and the symptoms were very obvious. The bike was extremely difficult to start, especially in cold weather—pressing the electric start button for a long time yielded no response, and sometimes I had to kick-start it several times. While riding, the engine shook violently, and the idle speed was unstable, causing intense body vibrations like an earthquake. Acceleration was uneven—stepping on the throttle resulted in weak power output, making it sluggish and struggling even on slopes. Fuel consumption also increased significantly; normally, a full tank could last 200 km, but that time, the low-fuel warning light came on at just 150 km, wasting extra money on gas. Incomplete combustion occasionally caused black smoke from the exhaust. Ignoring this issue could even affect the engine, leading to further efficiency losses. I recommend checking the spark plugs immediately if you notice difficulty starting, excessive shaking, or a sudden spike in fuel consumption—replacing them is quick, simple, and low-cost.

[MacLandon]

When spark plugs malfunction, motorcycles exhibit quite typical symptoms. Starting issues: Difficulty in cold starts or restarting after stalling, with noticeably prolonged cranking time. Engine operation: Severe shaking at idle, erratic RPM fluctuations, and strong body vibrations. Acceleration phase: Delayed power delivery, feeling like the throttle is engaged but the engine responds sluggishly, sometimes accompanied by slight knocking or backfiring sounds due to poor ignition. Fuel consumption and emissions: Increased fuel usage due to poor combustion efficiency, with possible black smoke from the exhaust. All these stem from ignition system failures. Ignoring them may lead to sudden stalling while riding, posing significant safety risks. A simple check involves removing the spark plug to inspect the electrode condition—clean or replace if fouled or eroded. Regularly change spark plugs as per the maintenance manual to prevent such issues. The cost is minimal, so don’t wait for a breakdown to act.

[DiEmilia]

Motorcycle spark plug issues can severely impact riding safety. Symptoms include starting failure: the bike won't ignite, especially frustrating during urgent situations when it stubbornly refuses to start. During riding: the engine vibrates intensely with unstable RPMs, the body shakes noticeably at idle, and there's insufficient power during acceleration, causing the bike to jerk or struggle to move forward. This may lead to loss of control risks, such as accidents occurring when power cuts out during turns or overtaking. Increased fuel consumption adds to the frustration, wasting money on gas and polluting the environment. I've witnessed a friend's bike stalling at an intersection, nearly causing a rear-end collision. Upon discovering the problem, immediately stop to inspect, replace the spark plug or seek repairs - never gamble with safety. Prompt handling can prevent further complications.