1978 L6 165 with 165 merc outdrive, was running wot fuel was low, all of a sudden engine boged down like it was running outa gas ,i slowed down to idle speed a few seconds put it to her again nose stands up almost to plane and same thing happens this continued untill finally she would just run at an idle , then would start back up but would die right out, outa gas right? well got towed back to marina ,got home put gas in her ran fine . but gas gauge read between 1/4 and 1/2 tank ,tank is 24 gallons i put 6 gallons in her. that should had only gave me 1/4 tank ,so i had gas still in tank so what would cause this problem .24gallons should give me about how many nautical miles ?i have noticed slight mph lately like 5mph . fuel millage is terrible . thanks. george