What Causes Loud Engine Noise in a New Motorcycle?

[AmeliaMarie]

Reasons for loud engine noise in a new motorcycle: Backfire sound: The noise is loud but not continuous. It manifests as the exhaust pipe backfiring and overheating during engine operation. The main cause of this phenomenon is an excessively small ignition advance angle, resulting in incomplete combustion of the air-fuel mixture in the cylinder. When the unburned mixture encounters heat in the exhaust pipe and spontaneously ignites or is ignited by a spark, it combusts and explodes, producing the backfire sound. Knocking sound: When the engine is running, using a "stethoscope" to touch the cylinder head reveals a sound similar to a wooden hammer striking, which is more noticeable at low speeds or when adjusting the throttle. This knocking sound is mainly caused by detonation or pre-ignition due to an excessively large ignition advance angle, excessive carbon buildup in the combustion chamber, or an overly high compression ratio. Misfire sound: This manifests as occasional one or two misfire sounds in the otherwise even and rhythmic exhaust noise during engine operation. This phenomenon is mainly caused by the sound produced by burnt or excessively small contact gaps in the breaker points.