how can i fiw my yamaha dtre125 2005 model?

i own a yammy dt 2005 model. but da bike keeps spluttering iv changed the spark plug but its still da same. when im riding it ill pull off in 1st and it will have a very slow start then i get to second and it will splutter and cut in and out. there is a split in da exhuast right at da back but iv been told it woodnt lose compresion there. iv also been told it may be the carberetta or sumthing in da jets but im still not sure wot to do ?? any help wood be appreicated. thank you