YPG-525 has 88 lightly weighted piano-style keys but YPG-625 has fully weighted piano-style keys. So YPG-625 feels more like a 'real' piano than YPG-525.
the difference is the Yamaha is better
the numbers
The Yamaha U3 is slightly larger than the Yamaha U1, this is the most significant difference. The larger size of the U3 results in longer strings and consequently to a richer and warmer sound.
The 620 is large bore while the 640 is medium bore.
Apparently the Paficica 012 replaces the EG 112 - that is the only difference
The model that you have listed is actually a Yamaha keyboard and not a motorbike. It can be purchased for approximately $500 for a used model. If you are indeed looking for a Yamaha motorbike there is a great deal of price variance between models.
the difference is the Yamaha is better
The only difference I see is the di version includes the ac power adapter.
The timing in the CDI unit.
the numbers
The Yamaha U3 is slightly larger than the Yamaha U1, this is the most significant difference. The larger size of the U3 results in longer strings and consequently to a richer and warmer sound.
about 25 to 35lbs depending on the year.
usually the difference is more sounds, probably more or less midi connections, maybe a floppy drive was added onto it, etc. if the numbers are a little bit higher than the other, not TOO much has been done, usually. if it were a bigger gap of number, or a higher set of letters from the alphabet, much much more is done, it'll be practically a whole new keyboard. more keys, more sounds, different color, bigger speakers. etc
J is 1982, K is 1983, carbs are the only main difference I think.
The 620 is large bore while the 640 is medium bore.
the L ,LWland LE has bigger tires than a E
Apparently the Paficica 012 replaces the EG 112 - that is the only difference