Yamaha - Carburetor Assembly 1 Fuel System Component YF1-26574-40-12. Overview. When a Yamaha starts idling rough or struggling under load, the carburetor is usually where I start looking. I've swapped out plenty of worn assemblies that just couldn't meter fuel the way they used to. The Yamaha Carburetor Assembly 1 YF1-26574-40-12 brings everything back into balance so the engine runs smooth and responsive again. It's a solid fix when cleaning and rebuilding just aren't cutting it anymore.. Key