My guess... Nothing. Guessing you're in the UK. These are the basics: Smooth drive boss, Up jet carb, de restrict the cdi. These will get you to 40 with no effort, and cost less than 20 bucks. A performance Variator, and Contra spring will get you close to 50 for about a hundred more. You'll want better tires than OEM as well. They are about 100.00 too. The rest gets into tuning, and expensive parts. Maybe 2-3 hundred for every 2-3 mph.