I am having trouble dialing in my carb on my 408w 5pd. I have tried two carbs 750 dp mech secondary and 750 sp (3310-4) with vacuum secondary both with fresh rebuilds. carbs are running way too rich (strong smell of raw fuel and black plug readings auotlite 45's). decent throttle response with no bogs. i have tried jetting down all the way to 68# jets and various air/fuel mixtures with number 5 and 6 power valves. i prefer not to switch to edelbrock. Any suggestions welcome. thanks.