The fact is I also ride/run other more modern 2 strokes with the same oil... and guess what?... I Never get carbon buildup (say... in my 250cc dirtbike)... the inside of the motor is spotless.
I also run it in an outboard boat motor.
I can't really say why... but remember... it took all of 5 minutes to clean this stuff out... so how bad is it ?
Remember also... this handmade exhaust pipe is over 10 years old.
For 3 or 4 times the price for synthetic ?... I'll clean the pipe every 10 years.
It MIGHT be because I usually ride the ped to the store and back... maybe it never gets hot enough ?
The regular gasloine I run ?... that has no effect whatsoever on this slight carbon buildup.
the reed valve ?.... here is the thing... this PA50I was the 'real slow' model... 21mph was all they did stock... I don't know why Honda made them that slow.
But 2 years later... Honda made the PA50II.. (very similar... but several small mods)
I am sure they had complaints from buyers of "why did you make this thing (the I) so slow ?"
They (PA50II) were near 30 mph stock... and one of the big changes was they went to a much higher flow reed valve... thats what I will be putting in early next week when I get it.
So the PA50I is kind of a special case... with a tiny, restrictive reed valve.
(a modern 50 would have about 6 times as much reed 'flow area')