Re: 40hp yamaha year?
Ive checked an I found "the letter". Its actually a 90mod. See the letter D in the bottom right corner.
What the numbers and letters mean:
No letter in front of 225 means two stroke
225 is hp
B means its a generation B(dont know what that is)
E stands for "Electric Start"
T stands for "Electro=hydraulic trim & tilt"
O stands for "Autolube Multipoint Oil [haggling] System"
6K7 means this series started in 1986 and is either a 225A or 225BETO
L stands for "Shaft Length: LONG"
350604 is the serial number
D means its a 1990mod.
In your case it says
6H4 and that means your outboard modell was first produced in 1983 and should be either a 40H or 40V?? (a litle bit strange since you say its a BETO)
Look again for the letter in the lower right corner. I didnt see the one on mine at first. Had to look closely.
I found the info
HERE
The text is mostly in english. A litle bit swedish, but youll get it.

Maybe google can translate.