Problems at mid range

[danielucioz]

Hello, i have a 2001 ec25 and when i ride at slow speeds and just a bit of throttle the bike does a back fire and if i dont full throttle for 3 seconds the bike after more 10 min of ride turns off and i need to change the spark plug. The plug when i remove it is full of gasoline. and when i try to rev in that 3 seconds the bike dont fully rev and smokes a little bit. after that is ok. And when i ride if i sometimes rev the bike to "clean" it rides completly normal. or if i ride just at high rpms the bike dont have any problem.

the carb is tunned with a 38 and a 168, the click of the needle is in the 1st

anyone knows what can be?

the oil mixture is at 1.8%