What is the gas to oil ratio for a 2003 yz 85?

It can be either 32:1 or 40:1. The 32:1 is a richer mix so if you are fowling plugs, switch to the 40:1. I run 40:1 and I have had no problems. 32:1 = 4 oz oil per gallon of gas40:1 = 3.2 oz per gallon of gas