What are the characteristics of a motorcycle's mixture being too lean or too rich?

[RileyDella]

Characteristics of a motorcycle's mixture being too lean are: 1. Difficulty in cold starting of the engine; 2. Unstable idle speed after running for a while, prone to stalling; 3. Lack of power at high speeds due to insufficient gasoline to produce greater combustion value; 4. Dry and whitened spark plugs. Characteristics of a motorcycle's mixture being too rich are: 1. Increased fuel consumption, with too much gasoline not fully burned; 2. Popping sound from the exhaust pipe when decelerating at high speeds, the bike has power but is difficult to restart after stalling when hot; 3. Black smoke from the exhaust pipe, higher engine temperature, excessive combustion temperature damaging valve components, and darker engine oil; 4. Carbon-fouled spark plugs and more carbon deposits inside the cylinder.

[AdrianaMarie]

Last time I rode my bike to the mountains, I clearly felt that even with the throttle fully twisted, the speed wouldn't increase, and the engine emitted a sharp high-frequency noise. The exhaust pipe was frighteningly hot. The mechanic said these were classic symptoms of a lean air-fuel mixture—too much air and too little fuel, causing slower combustion and engine overheating. Conversely, when the mixture is too rich, the bike behaves like it has a bad cold, with black smoke puffing from the exhaust and spark plugs covered in black carbon deposits. At idle, it shakes so much even the mirrors dance. The most frustrating part is the drastic increase in fuel consumption; it's normal to get 50 kilometers less on the same tank of gas.

[VanJayce]

My old motorcycle has been acting up lately, requiring the choke to start when cold, and frequently stalling after warming up. Uncle Wang at the repair stall said it's due to an overly rich fuel mixture, where too much fuel is injected and doesn't burn completely. After one carburetor adjustment, it started behaving differently—the engine sounded weak when climbing hills, throttle response was sluggish, and the spark plug electrodes turned pale white after a ride. Now I understand that fuel mixture is like seasoning food: too little lacks flavor, too much overwhelms. Beginners often trip up on small issues like sticky needles or clogged air filters.

[Daniel]

After riding motorcycles for fifteen years, I can diagnose the air-fuel mixture condition just by looking at the exhaust pipe. If the exhaust port is covered in black soot like a coal briquette, it's definitely running too rich—too much fuel, not enough air, resulting in incomplete combustion. If the pipe is so clean it shines but the bike struggles to accelerate, it's likely running too lean. The most obvious signs during hard acceleration are: a rich mixture causes a muffled roar with black smoke, while a lean mixture results in the engine screaming without moving. Yesterday, I helped a neighbor adjust his carburetor. His bike's air-fuel ratio was so messed up that the spark plug showed a stark contrast—the center electrode was eroded and white, while the threads were caked with carbon deposits, like a pair of 'black and white demons.'