Jetting is not the answer- both of mine have had dead stock jetting and started right away in temps down down in the single digits even after sitting outside all night. Make sure the choke is all the way out, and that is STAYS all the way out (twist the rubber ring around the choke shaft clockwise to increase tension on the shaft so it stays put). Do not touch the gas, and hit the starter button. If it still does not fire right up, make sure the choke is adjusted correctly so it is enriching both carbs equally.
