Why didn't the five-speed Changan van speed up? The fastest run is 80, please ask professionals to answer?

1. The throttle valve is too dirty and needs cleaning. 2. The spark plug is insufficient and needs to be replaced. 3. Insufficient air intake and insufficient combustion. The choke is too dirty and needs cleaning. 5, poor exhaust, gambling plug. 6. The engine timing is incorrect and needs calibration. 7. There is too much carbon in the engine combustion chamber, which needs to be cleaned. 8. The engine piston ring is poorly sealed and leaks air. 9, gasoline pump pressure rise, or pressure relief. 10. If it is a carburetor car, consider cleaning the carburetor. Please check according to the above method, absolutely good! !