just bought my son a 2004 txt 50 boy and it runs great until its hot, say 15 mins riding ,then it will not rev correctly and sounds as if its either missing or running out of fuel and also has no power. If I stop it for 3 mins then kick it into life it runs great again for 15 mins??? Has anyone had similar problems with this bike? Oh and while i'm here does anyone now which friction plate I must change to enable the clutch to engage sooner?

Electrics, these bikes are known for having problems with the stator. the symptoms you describe are what happened to my daughters.Give Gas Gas UK a ring and they should be able to supply a re-worked stator or they may put you in contact with someone who can sort it.Ours went off to spain I beleive to be sorted and it has ran perfectly since.