Hi Akhor,

Someone will correct me if I am wrong, but I think the "Gen4" "Gen5" only applies to the Pro motors, ie 3 port RSpec, 5 port, 7 port etc.
The easiest way to tell the difference with these motors is the logo's inscribed on the cooling heads. The Gen5 motors have more writing and the new style Go logo. Internally they are quite different with the newer Gen 5 models having a new style carb, new crank, new style cooling head and some minor changes to the crankcase design. Cheers