As far as whether the manufacturers used the main jet size as a form of governor.
Back a while ago when Evan posted about his engine (Puch Maxi) "4 stroking" at top end.
Then Tony accurately described all the symptoms of too rich a main jet but said he wasn't convinced it was too rich of a main jet..... but that the same problem had cropped up several times in the last year on this forum with no clear solution.
That was when I began to believe that the European manuf. might have looked at the US market with its restrictions on speed and HP and might have decided that the best (and cheapest) solution was to simply put too big a main in their Euro spec peds and meet the US spec's.....(too big a main preventing the ped from revving out and making more HP and speed... like it should)
They probably figured that anybody would figure this out quickly (after all they are experts.... isn't everybody?) and rejet leaner to get back to correct performance and speed.
But the truth is a lot of moped dealers (especially Euro peds) have very little mechanical knowledge and just want to sell them and make money.... so they might not have any idea what to tell his customers when they come back wondering why it doesn't seem to run right.
The Jap manuf peds are sold at motorcycle dealers with good service departments... and I beleive the Jap peds are designed specifically for this market (in some cases) and are not "muzzled" when they leave the factory.
But I do know specifically of 3 Jap motorcycle models that are intended to be modified immediately if you want full performance... by removing restrictors, or switching to a different exhaust pipe (included when you buy the bike).
I have limited experience with Euro peds... that is why I am mostly guessing at this as a possibility.... but I almost posted this exact note here a couple days ago... the Ron brought it up !!