lanow

Hi Everyone, I am new to this forum and hope that someone out there can help me, I have an early Suzuki King Quad 300 (280cc) which starts intstantly every time but at about half revs or there abouts it starts spluttering and will not rev any higher, this fault is present whether choke is applied or not, some one suggested that silencer maybe be clogged so removed baffle but no improvement have removed carb and stripped 3 times but still no joy. Any ideas would be most welcome. Cheers Rob