Try this http://www.tytrials.co.uk/blog/read_12974/date-your-ty.html

If the link doesn't work it looks like yours is a 1976 TY250C

Here is the most complete listing I have ever seen.

http://www.yamahaty.com/english/serieen.html

hello there,

i have just bought a ty250, with frame number #493-30---- making it a 1977 model but road registered on a "C" as first registered in 1986/7.

i am hoping to do some long distance trials (LDT's) if any one has any advice on setup etc.

many thanks

phil