It can't be used for Yamaha Series. Shaft gear: 19T (as per the 1st picture). NO installation instruction and recommend professional installation. The item "Universal Go Cart Forward Reverse Gear Box for vertical 125-300CC engines" is in sale since Friday, October 9, 2020. This item is in the category "eBay Motors\Parts & Accessories\Performance & Racing Parts\Auto Performance Parts\Engine & Components\Racing Engines".The seller is "ytmoto" and is located in Yongkang, Zhejiang. This item can be shipped worldwide.