The crap fuel has probably plugged up the idle circuits. The carbs need to be removed to clean them properly, and that is best left to someone with experience. The carbs on your motor don't really have "adjustments". Once they are synchronized they ahould be left alone. Get into the habit of popping off the fuel line when you put her back on the trailer and let it run itself out of fuel (lower unit still in the water of course). It will save you hundreds of dollars in the future. And yes...Get rid of the 1/4" fuel line. It's too small for a v-6.