fit full arrow exhaust system. Fit 320 main jet. Fit fibre reed in the reed valve. Modify powervalve so its fully open at high rpms. A yamaha dealer will derestrict for you. These will give around 28bhp. Once this been done change the gearbox sprocket for 18 teeth or the rear wheel sprocket for 51 teeth (only change one of them). Top speed will be 95mph at engine redline. Downside is 90 miles out of a full tank of fuel. check out http://yam2stroke.free.fr for more info