For my 410 sb I am using a 850 ultra and when we ran the motor on the break in stand it was filthy rich.Black plugs,bit of smoke out the pipes,ect.The carb comes with 84 jets all around and 4.5 power valves front and back.I know I have to go leaner but how much?The motor is 410 ci,ported eddys(flow 270 int)10.5 to 1,flat tappet solid,602/624, 262/274 @ .050 inst @ 104.Victor intake,2" spacer.I was thinking maybe 76 jets?

Here is what I would try as a starting point, in reasonably good air: 78 jets in the primaries with PV, leave the 84s in the secondaries and take secondary PV out. If you feel that you need the PV in the secondary side, use 78s there as well.

I have never seen power valves in the secondary,is there a reason for them?

I have a 950 ultra HP, do your self a favor and get a wideband.

What boosters are in your 850? down leg , annular?

Look at leaning down the idle and transition circuits first Most of the stock Holley D.P. and Domnator are way to fat on the idle and transition circuits for most Mopar V8