Does anybody know how to interpret Chinese engine model reference numbers?.

I know the first numbers appear to indicate capacity, but sometimes the number changes not because of different displacement but to indicate that it has a balancer. What do the letters mean, for example on a number like 156FMI?

So far I have this for the prefix numbers:

139 is 50 cc
147 is 90 cc
150 is 100 cc
152 is 125 cc horizontal engine (Honda Cub type)
154 is 125 cc " "
156 is 125 cc vertical or sloping single (Honda CG125 type)
157 is 125 cc vertical with balance shaft
161 is 150 cc
162 is 180 cc
169 is 200 cc