Karoo to sttava VERY inaccurate versus garmin watch

When done cycling both. My garmin watch and my karoo upload data to strava. Distance and time are the same, but watt and calories diiffer greatly. Eg 58k / 2,5hr /81kg garmin says 1400 kcal karoo (better strava bases on karoo fit file) comes at 2300 kcal. Strava also calculaties the watt at 240.i would be Very happy if this where True. Hoe can i get karoo to supply better data to strava?