What are the reasons for a underbone motorcycle not accelerating when throttling?
2 Answers
It may be caused by a lean air-fuel mixture or failure to warm up the engine after starting, resulting in poor throttle response. This phenomenon in motorcycles is called high-speed misfire, where the spark plug fails to ignite continuously at high RPMs, leading to jerky acceleration or inability to reach high speeds. Backfiring is the most obvious symptom, as unburned air-fuel mixture is expelled into the exhaust pipe due to misfiring. When this mixture ignites during the next cycle, flames are expelled, causing the backfire. It is recommended to first adjust the clutch clearance, as there might be clutch slippage issues. If this doesn't help, replacing the entire clutch assembly should fix the problem. If the engine RPMs still jerk when revving in neutral, it indicates an ignition issue. Check the ignition timing, and if that's fine, try replacing the ignition coil.
I've been repairing motorcycles for over 20 years, and when it comes to acceleration issues in underbone bikes, we usually start by checking the fuel system. A dirty carburetor is often the culprit, as an imbalanced air-fuel mixture directly affects combustion efficiency. Fuel line blockages are also frequent troublemakers - clogged tank filters or faulty fuel valves can cause insufficient fuel supply. If the air filter hasn't been replaced in three years, it's likely packed with dust, restricting airflow and sapping power. In the ignition system, carbon buildup on spark plugs or aging ignition coils can reduce spark energy. Worn clutch plates causing slippage is another common issue preventing power from reaching the rear wheel. For such cases, start by cleaning the carburetor, then inspect the air filter and spark plugs - this usually solves the problem.
