Re: 25 hp evinrude backfires
YOu did not mention year or model number of the engine.
If you have point ignition try cleaning the points and re setting them, been known to set up just over the winter months and need cleaning to et running again (same way with my old 1948 Ford 8n).
If you do not have a point ignition then as TD said 99% it is carbs but you may want to lok at your connections and make sure none are corroded andf that your batery is charged good and full if electric start.