Symptoms: A technician reported that a 125cc scooter (with a GY6 engine) has difficulty starting when the engine is cold. After starting, the engine runs unevenly for the first few minutes, but once it warms up, it operates smoothly and starts easily. The technician conducted multiple checks: cylinder compression and seal were normal; the spark plug produced a good spark between its electrodes; fuel flow was unobstructed; cleaning the carburetor did not resolve the issue; replacing the ignition coil, igniter, charging coil, and pulse trigger coil also failed to fix the problem. Even after changing the engine oil and injecting a small amount of oil into the cylinder through the spark plug hole, the issue remained unresolved. Fault Analysis and Resolution: Based on the technician’s description and the characteristics of the “electric heating type automatic start and enrichment device” installed on the carburetor, it was suspected that the root cause was related to this system. Specifically, the needle valve of the enrichment device was unable to open during cold starts, preventing the air-fuel mixture from being enriched properly. This made it difficult for the engine to start in cold conditions. However, since the engine ran smoothly when hot, no other components were found to be faulty. Upon removing the carburetor and inspecting the system, it was discovered that the needle valve of the electric heating enrichment device was stuck. After clearing the blockage, the engine started easily even in cold conditions, idle speed became stable, and acceleration responded quickly. The fault was successfully resolved. It is worth noting that when the power supply to the electric heating enrichment device was disconnected, the engine started and ran well when cold. However, once the engine warmed up, the mixture became too rich, leading to poor performance, difficulty in starting, and rough running. This highlighted the importance of the enrichment device in adjusting the fuel mixture during different temperature conditions.

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