hi i have a 49cc air cooled cag bike and for the last three weeks it has been running fine unitl the last few days. it runs fine for the first 3 or 4 minutes then once it hit full revs it starts to sputter as if it running out of fuel if u take it bak to half accelaration its fine but if u leave it at full revs the bike stalls. but as soon as u pull the starter it starts fine until u hit full revs agian. any help would be appreciated.