What is the reason why the scooter cannot go beyond 60 mph?

[MacAvery]

It may be due to issues with the electronically controlled choke and vacuum diaphragm of the carburetor, or the negative pressure fuel tank switch being damaged, causing fuel to flow from the suction pipe and resulting in an overly rich air-fuel mixture. Here is some relevant information: Types of motorcycles: Fuel-powered scooters belong to the motorcycle category. Those with an engine displacement below 50CC are classified as light motorcycles, while those above 50CC are classified as regular motorcycles. License plate differences: Regardless of the type, corresponding license plates and driving licenses are required for legal road use. Light motorcycles have blue license plates and require an F-class or higher driving license; regular motorcycles have yellow license plates and require an E-class or higher driving license.

[Lulu]

I've been repairing scooters for over a decade. The most common reason for not reaching 60 km/h is aging transmission systems. A stretched, slipping belt is like running in shoes two sizes too big, while worn variator rollers keep the transmission stuck in low gear. Just this week, I helped a customer by replacing their belt with a Taiwanese-made reinforced one and upgrading to 15-gram heavier rollers - the scooter immediately hit 85 km/h. If the clutch shoe springs are loose, they can't grip the clutch bell properly, causing howling noises during hard acceleration. Check your belt width yourself - new ones are 20mm wide, and should be replaced when worn down to 17mm.

[MacLyla]

Last time my Jog was also stuck at 60 km/h. When I opened the air filter box, I was shocked—the filter element was completely clogged with willow catkins, turning into a felt cake! At high RPMs, the air intake couldn't keep up, causing the fuel mixture to become too rich and resulting in power loss. After cleaning it with a high-pressure air gun, it immediately restored to 70 km/h. Now I make sure to replace the filter element every 2,000 km. I also cleaned the throttle body—the backside had oil sludge so thick you could write on it. For carbureted bikes, you need to adjust the needle height; for fuel-injected models, you have to check the throttle opening data. If you don't have the equipment, it's best to visit a workshop to read the fault codes.

[Paislee]

My friend's NIU NQI was stuck at 60 km/h during a test ride last weekend, and my first thought was a fuel system issue. The filter screen at the bottom of the fuel tank was clogged with rust, making it hard for the fuel pump to supply fuel properly. After removing the fuel pump, I found the bellows were completely sucked flat. After replacing the filter screen, the fuel pressure increased from 2.1 to 2.8 bar. If the injectors have been modified, they need to be checked as well. Upgrading from a 125cc to a 150cc cylinder kit without changing the fuel injectors will definitely cause insufficient fuel supply at high speeds. For older bikes, it's also important to check if the vacuum hose is leaking.

[Roger]

In my modification shop, we often encounter this situation: the exhaust pipe catalyst is clogged. The original exhaust pipe core is like a honeycomb, and when carbon buildup is excessive, it's like running with a mask on. Once, we cut open a Chery 150 exhaust pipe, and the fragmented catalyst carrier completely blocked the tail section. Using a mirror to look into the exhaust pipe outlet, if the smoke ejection is weak during acceleration, it indicates a blockage. Additionally, pay attention to ECU speed limits. Some China IV vehicles control the top speed via the ECU. When testing wheel power on a dynamometer, anything below 6 kilowatts definitely has a restriction.

[Etta]

If you notice a lack of speed, first check the engine temperature. My Cruisym 150 experienced overheating protection during mountain rides because the cooling fins were caked with mud! After blasting them with a high-pressure washer, the temperature dropped by 10°C. A clogged transmission vent due to mud is even more critical, causing clutch slippage from high heat. Also, tire pressure matters—front tires at 1.7 bar noticeably struggle to accelerate compared to 2.2 bar. Fitting wider tires without changing the gear reduction ratio is like hitching a horse to a cart. Don’t forget to check the oil level—an extra 100ml of oil can sap two horsepower.