Hi Peach,
sounds like the problem i was having up until two weeks ago.i had it back to the dealer eleven time's between 02/12/08 and 19/02/09.i had to do alot of kicking+screaming but it seems to be sorted after they changed the trottle positioning sencer.i ended up ringing danfay(yamaha ireland)and got on to the warranty's man there(martin)explained my problem and that the dealer i bought it from could'nt fix it and that he would be receiving a letter from my legal council.so danfay picked it up from the dealer and brought it back eight days later,and it works now so i'm happy.