Yamaha Models of the 15 hp 2 Stroke

I bought a '83 15 hp Mariner and was pleasantly surprised to find out it was pure Yamaha, and not a Tohatsu. Around here Yamaha are considered the best little outboards. Google has been very unhelpful, here's question for an Yamaha expert , what years did Yamaha models change ? And the changes ? I know from experience there is quite a difference between a '74 and a '76 Merc 7.5 . This would be a great help in getting manuals and parts. I don't think Mercury would be very enthusiastic about Yami / Mariner support from what I did find on Google

What difference is there between a 74 and 76 Merc 7.5 ??----Post some details.

The differences between the Mercs are ignition; cowling, upper and lower; clamp bracket, clamps; swivel housing ; stainless steel drive shaft, shift rod , maybe the prop shaft too; front fascia ; and the important one, decals. One has blue strips and the newer one blue bands. These are Canadian models. Shouldn't this be on the Mercury forum, though.