hi folks i,ve got a formula ls242 with a 502 mercruiser. now i know i,m not going to get good fuel economy with it, but it drinks fuel like its just been invented, so i put a colour tune in it and its mega rich, i can tell its running rich by the way she starts and idles.tried cutting her down with the mixture screws but they make no difference, colour tune is still orange and she still runs lumpy. choke etc is off,checked timing,new plugs. any ideas on carb problem. thanks ged.