What causes a motorcycle to not accelerate when the throttle is applied after starting?

[McRonan]

Motorcycle fails to accelerate when the throttle is applied after starting due to lean fuel mixture or poor crankshaft case sealing in two-stroke engines. Specific reasons are as follows: Lean fuel mixture in motorcycles: A lean air-fuel mixture results in insufficient gas pressure acting on the piston after ignition, prolongs combustion time, and causes engine overheating. Symptoms of a lean mixture include poor acceleration during operation, which improves when manually adjusting the choke or pumping fuel. However, acceleration weakness reappears without enriching the air-fuel mixture. Poor crankshaft case sealing in two-stroke engines: Air leakage due to failed crankshaft oil seal on the generator side; air leakage at the crankshaft case midline joint; air leakage at the interface between the crankshaft case and cylinder, or incorrect piston installation direction.