If you haven’t heard that acronym before it stands for Finest Year K. It refers to 1985 United States K100s which have “Euro” cams which are “hotter” than the cams in 1986+ US K100s and put out something like 5-7 more horsepower. However, the 1985 K100s were not compliant with California emissions standards so from 1986 on all US model bikes had “de-tuned” cams and fuel tank venting back into the front of the engine block in order to be California compliant.
The California cams (11311461525/11311461526), as well as the normal or “Euro” cams (11311460045/11311460044) do show up in the parts catalog but, unlike most parts that changed over time, there are no from/to dates so you can’t decode your VIN to figure out what engine/cams you have from the production date.
Since part numbers aren’t cast into the cams, you can’t simply inspect the cams to tell which you have. (If you’re a real mechanic with a real shop you could measure them and tell the difference but most of us aren’t.)
Anyhow, since part of the changes on US bikes from 85 to 86 was to add the venting line from the gas tank to the front of the engine block, the easy way to confirm if you’ve got an FYK is to look at the front of the engine. If don’t see the gas tank fume vent fitting on the front of the top of the engine then you’ve got an FYK.
I’ve attached a couple of pictures copied from Fleabay K100 engines for sale as visual aids.