The F2 & F3 engines are identical, but the frames differ a little bit. There's more F2 than F3 out there. The F3 wiring, if you run into mysterious wire colors that don't make sense, came from the next-generation CB750K DOHC chassis, after the first few months of production. Thus, you might have to cross-reference between the 2 wiring diagrams in some cases. Some of the F2 came without the odd little oil cooler in between the oil filter and the engine, but all of the F3 had them. Honda was trying to reduce the fast-wearing valve guides by cooling off the oil a little bit. In reality, the problem was their Jinglish mis-translation of the oil requirement in the post-1974 Owner's Manuals: someone accidentally wrote to "use 10w40 oil" when it was supposed to say, "Use NO LESS than 10w40 oil", and 20w50 was normally recommended. Thus, many of the post-1974 bikes have worn-out valve guides, cam bearings, and other oil-related issues, usually by 10,000 miles or so. With proper oil, they can last over 60,000 miles, easily.
quoteing Hondaman
