Across Europe, post-WWII veterans removed every part that wasn't necessary and modified their motorcycles to make them faster to race outside of cafes for bragging rights. Known as Rockers or Ton Up Boys, they were the British equivalent of American Graffiti and their café racer motorcycles became synonymous with the brash men who raced each other on motorcycles from one café to another at speeds near 100 mph, known as "the ton." So if you are looking to convert your vintage motorcycle into something more café raced out, start by doing some research.
Originally café racers were British twins like Triumphs, Nortons and BSA, but if your motorcycle's look looks a little tired then spruce it up with a café racer look. One of the first things café racers did was remove any unneeded part. Unless the law requires them, remove conveniences like mirrors and turn signals as well as chain guards, fenders and superfluous gauges or switches. If you are going to use a mirror, buy a retro Napoleon Bar End Mirror. Keep track of your speed by wiring up a minimalist bicycle speedometer for $15. After removing all of the bike's unneeded weight, café racers sought performance to go faster then the next guy. Removing their stock handlebars, flipping them end over end and reinstall them upside down, gave café racers a more aerodynamic riding position to increase the likelihood of reaching "a ton," or 100 mph. Modern riders can buy a set of Clubman bars to give their bike the same look.
To further aid their aerodynamics, café racers would install small gas tanks since they were only racing about town. Look at online sites like Craigslist or eBay to find a smaller tank that fits your look. To further solidify the café look your bike is going to need a single, stainless steel headlight that mounts to your fork stanchions. Expect to spend $50 for a headlight that uses a modern H-4 bulb and another $20 for the accompanying bracket. Now that your bike is looking and riding the part make it sound like a café racer by removing some of the packing in the exhaust cans. This will help the bike breath a little easier while making the bike sound a bit sharper. Top off the look by getting yourself a black leather jacket, tight Levi jeans and leather boots so you can look as authentic as your bike does now.