ORIGINAL: w8ye
Typically this involves minor differences as to the throttle arm, purge pump, angle of fuel inlet, etc
I have engines with all 3 versions of the WT-76 and though I have not compared them for the exact differences, I did note that 2 of the versions were made in different countries. That was Mexico and Japan. One version had different length needles. They all run pretty much the same with needles that have a nice broad range of adjustment and good idle ... midrange ... HS transitions.