i´m having a slight problem with my zy250f, i bought the bike brand new it runs great once its going but it seems to bog down and backfire every time i ride with the choke off. there for in order to ride it only preforms with the choke on . iv changed and clean the air filter to ´´uni´´ change oil, running engine ice coolnt , it make a good difference but still bogging out .... please help i need to know if i need to re jetted it and what size jets should i go with