Ford, Nissan, Dodge, Toyota all run 2 plugs per cylinder on the 4 cylinder engines to help with emissions.
80's Yamaha 650's ran 1 coil to fire both cylinders with one pickup coil. As one fired on compression, the other would fire on exhaust. No extra noise, and it was primarily to help with fuel burn.
One would think as it fired on the exhaust, it would pop out that side, but mine never did that. Ran really good, especially after I uncapped the mixture screws and set them equally for both cylinders. I was getting in the high 50 MPG with mine. The gearing was pretty good which helped. The final ratio was 2:1, 17 tooth primary, 34 tooth final.
She would get up to 60 in second gear pretty easily.
I hated to sell her, but I'm looking to get another one, but when I do, it's going to be an earlier model with points and dual coils. Easier to work on, and can get better performance out of them.