Moped Army

I just fired my sachs for the first time this year...
i think it made the same thing last year, but now i need to know why.

My moped is a sachs g-4, everything is STOCK!
my filter is clean, and no big restrictions... except for original ones...

i made a plug chop with filter, and the plug was WET AND BLACK
so i'm telling to myself... must not receive engough air...

for fun, i remove my filter, and do another plug chop...
the color is a sweet light brown, probably a little to light, should be a little bit richer i think.

here's what i checked/did:

-my choke isnt stuck.
-i'm using original jet.
-all the bolts are tight, near the carb and engine
-i cleaned the carb, at least 4 times.
-my airbox is clean

i'm sure someone here can help, it's probably a simple question, but i cant seem to find what's happening.

without the filter, it runs like a dream... but... i dont want to ride it without the filter, and i want it to run well...

anyway, any help will be HIGHLY appreciated
thanks a lot!!!

G.B.