kymco scooter runs for a while then dies?

i just got this scooter from a buddy who owed me $ and it didnt run and i changed the spark plug cause it was all gumed up so i changed it and it ran liek a champ and i drove it around for 2 hrs around town it ran fine and then 2 ppl get on it runs fine for 15 mins and they come back walking it its still kinda running but when i gas it it kinda bogs down not totally if i let off the gas it will idle but once i give it gas it kinda bogs any ideas?

no one has these scooters i see them all over no one have experience with them?

i checked for fuel and spark and ihave both spark isnt crazy bt it has some so i figured since i drove it it got fouled out so i cleaned carb out and i got a new plug and now i got no spark with the new plug. never had problems ever with the ngk plugs and so i tried the old plug again and i do have spark but its little nothin like car coils