Is my 340 Overcarbed? Avg 5-6 MPG

OK I see what you are talking about now. I just got out the instructions. It looks like I have either a blue or black one installed. I cannot tell from the underside cause its a tight fit and dark, but looking at the left over bushings I cant tell if the spare is black or blue! LOL! My neighbors are mad at me right now for running this so late so I am calling it a night. I will mess with it some more tomorrow. I am learning here. OK I will set timing up at 23 and do as you suggested. Thanks again for all the help.