The Fastest Upgrades for a Metropolitan Scooter

by John Willis
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The Metropolitan is a popular line of scooters from Honda. The 50 cc Metropolitan is good for a maximum speed of 40 mph, averaging 100 miles per gallon or more. Fun and nimble, the Metropolitan's performance is more about convenience and gas mileage that speed. However, there are several quick and easy ways to upgrade a Metropolitan, CHF50 scooter.

What You're Starting With

Until recently, scooters have been powered almost exclusively by two-stroke motors because of their high power to weight ratio. Metropolitans have 50 cc single cylinder four-stroke engines, but demonstrate power comparable to the 50 cc two-stroke engines that preceded them. Upgrading a four-stroke engine is a fundamentally different process than upgrading a two-stroke engine. It is also typically more expensive because of the relative complexity of four-stroke valve-trains. One way has already been done by Honda: a high, 12:1 compression ratio. However, there are other upgrades that you can make yourself.

Exhaust Flow

Letting the exhaust (and the whole head) flow more freely is the way to build more power. These are the fastest upgrades (versus machine chops, camshafts and valve porting). These are bolt-on upgrades that quickly provide better performance. Take the old one off, put the new one on and the system is instantly faster.

Exhaust Flow

While increasing flow increases performance, the most restrictive area of the head limits a motor. A high-flow exhaust won't do you much good if the engine cannot breathe air in. Carburetor jetting, modifying or upgrading can provide significant performance gains. Again, we are talking about fast upgrades. There is no faster performance upgrade than a high-flow air filter. Coupled with a high-flow exhaust system, the two upgrades should increase your overall head flow.


A performance tuned aftermarket variator is unique to scooters---or any vehicle with an automatic clutch. The variator is a device that engages and transmits engine power to the rear wheel as the engine revs. High-performance variators not only wear better, with increased speed relative to Original Equipment Manufacturer (OEM) units, but they can be fine-tuned for speed, versus acceleration, to suit your specific riding needs.

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