E85 Tuning Tips Because pump E85 can vary seasonally in some geographic areas, it may be necessary to adjust jetting or air bleeds to maintain the best possible tune up if you do not run your own blend. In some areas the ethanol content increases in the summer time and the gasoline content increase in the winter. This change in fuel blend was intended to help with cold weather start up in flex fuel vehicles, but can adversely affect non-fuel injected cars converted to E85 if