Please realize that I am not a VIN expert but in the last few weeks this is what I have taken from the internet.
"Thus 1980, 1981, and perhaps even some very early production 1982 model-year bikes use a shorter VIN number that appears on the frame of the bike, and may also include a printed paper decal that lists a different (longer) VIN number that is the "extended", 17-posiiton version of the original, shorter VIN number.
Although for the purposes of absolutely, positively identifying your bike for exactly what it "is", the differences between the shorty VIN and the longer VIN are minor---although since the full 17-position VIN number contains more information, it makes the deciphering process a bit less time-consuming, but rest assured that----armed with the proper information---even a "shorty VIN" can be just as accurately and fully de-coded.
Now, since most people weren't about to memorize serial number ranges, a second method was devised by Yamaha to code the year model into an easy-to-understand code.
In naming their bikes, Yamaha would refer to bikes by their MODEL NAME (i.e. XJ550, XJ650, etc.) and then add a---you guessed it---a LETTER CODE to the end of the model name, as such:
XJ550H
XJ750J
XJ900RK
Unfortunately, the letter codes used in this manner bear no relation to the letter codes used in the 17-position VIN schemes.
Here's the shorty Yamaha letter codes:
A = 1974
B = 1975
C = 1976
D = 1977
E = 1978
F = 1979
G = 1980
H = 1981
J = 1982
K = 1983
L = 1984
N = 1985
S = 1986
A couple of things to note here:
a) Prior to 1974, no code was used to designate the model year.
b) The letter I is skipped from the 1981-1982 sequence.
c) The letter M is skipped from the 1984-1985 sequence.
d) The letter O, P, Q, and R are skipped from the 1985-1986 sequence.
So the Yamaha coding system for identifying a particular bike was the use of the MODEL NAME (XJ550, XJ750, etc.) and then adding a year "suffix" at the end:
XJ550H is a 1981 XJ550 Maxim (the letter "H" = 1981)
XJ750J is a 1982 XJ750 Maxim (the letter "J" = 1982)
XJ900RK is a 1983 XJ900 Seca (the letter "K" = 1983)
Uh-oh........that last one is a bit confusing (there's two suffixes....R and K).
Well, to distinguish between a regular Maxim model and a Seca (or other) model, Yamaha also used other suffixes:
nothing = a regular base model (Maxim is the base model in the USA and Canada)
R = Seca
C = could mean Canadian, or could mean California. Nice, huh?
M = Midnight version of a Maxim, if it's an XJ750, but "L" if it's an XJ650 model, unless, of course, it's a 1982 or 1983 XJ650 model, in which case "L" refers to the Turbo Seca model, and..........
L = any one of a number of different things....
I think the best thing we can say is that "perhaps it's better than nothing".
Perhaps.........
The key point to remember is the letter codes above refer to the years."
Preceding information taken from a thread on XS650.com
Also some information for cross referencing Yamaha factory model codes to actual model numbers is at ?johnnystoybox.com?.
Hope this helps!
Shep
