I have checked and they are the same - hence the question
(Nathan, never start an arguement you havent already won)
Making allowances for stuff that can be freely modified/swapped under the existing rules (like wheel diameters and shock absorbers and fork internals and cosmetics).
The 1990 YZs got different forks to the '89s (including a different colour, making them easy to spot). The '90 YZ250 got a significantly different frame, with different radiator mounts, different swing arm and different rear suspension linkage, and a different barrel.
It is not a carry-over bike, and would be quite easy to pick someone trying to slip one through.
The 1990 RM250 got a different frame, with rectangular section tubing near the swing arm pivot.
It is not a carry-over bike, and would be quite easy to pick someone trying to slip one through.
Both the 1990 YZ & RM 125s are close to being 89-model carry-overs, although they both got different forks to the 1989 models, making them easy to spot.
I'd contend that with the right forks fitted, both would be acceptable Pre-90 bikes - and as the 90 RM125 forks are essentially the same as the 89 RM250 forks, then a stock '90 RM125 should be an acceptable pre-90 bike
(bit vague on that, because a 14 year old Nathan cut up his now-valuable reference material, so I can't tell you about the 90 RM125 motor compared to the 89 model's). Compared to the 90 models, the 91 RM125 & 250 got bigger forks (45mm), and different & linkages swingarms to the 91s. The 125 also got a different barrel.
91 YZ125 & 250 had similar upgrades to the RMs, along with a different frame to the 91s.
So none of the 91s are possibly carry-over pre-90 models, even if the 1990s are.
Kawasaki made it easy to spot a 90+ KX125/250 from the pre-90 models by going to the perimeter frame. The KX500 IS a legitimate carry-over bike, providing it has the right model forks - same goes for the CR500, I believe.
The CR125 went to a HPP exhaust power valve in 1990, easily distinguishing it from the pre-90 models.
CNBF looking at the 1990 CR250 right now.
The idea that it is impossible to pick the differences between post-84 model bikes, is a myth. The knowledge will be gained as the knowledge is needed.
99% of the general population wouldn't know that a 1977 CR125 isn't a legal pre-75 bike while a 1975 model is - but
we know because we know what matters and what to look for.
Similarly, I have SFA idea about the legalities of pre-65 bikes, but the people who are interested and/or who need to know, know.
