ive brought myself a cr 250r 03 model and im having trouble with the plug fowling up ive been told to run the petrol mix at 33/1 but when i do this the plug fowls up and the bike wont start. it seems like when i run the mixture at25/1 it runs great but ive been told it could hurt my rings could anyone please tell me the right mixture to run my bike on or maybe add a sugestion....