RD350 F2 1986-1991
These were the last of the line produced by Yamaha. Again F and N was for Faired and Non-faired.
Everyone expected this model to be significantly more-powerful than the 31K because new RD models had always brought more performance. Well, the new expansion-chamber style exhausts certainly promised better performance because they can produce much more power than the old 'cigar' exhausts of it's predecessor. However, to meet new emission and noise regulations, the engine was redesigned to produce peak power at a lower rpm than the 31K, which reduced the power. This largely offset the gains from the expansion chambers, which were themselves designed to work best at lower revs to suit the engine.
The net result was around the same power as the 31K but an engine that would not rev freely.
The engine modifications to reduce the rpm where everywhere: in the cylinder block; ignition; electrics and the cylinder head, as well as the aforementioned exhausts. As a result, these models are much less popular with tuners and racers because almost everything needs to be changed to get back the rpm, which is needed for maximum power. It is easier to tune the earlier 31K, which already revs freely.
As you would expect, Yamaha were not going round trumpeting that this was a slightly de-tuned but more environmentally friendly version of the bike. That didn't fit the image. As a result, plenty of people today still believe that this bike is more powerful than the 31K.
The 1WT engine number prefix gave them the monica of 1WT.