I am not sure why it does that but my original 21 was exactly the same.It would idle fine but be realy slow until it had got to around 200f then it would scream and wheelie everywhere.I am no tuning expert but i reckon its down to getting it very finely tuned.I just put up with mine until it had warmed up but i am sureMel,Madmanluke and others on here will be able to give better advice as they know savages inside out .Hope this helped a bit.