1st off the 450's you have are mechanical secondary. Most 450's that people run are vacuum secondary. I have the same carbs. I run mine with progressive linkage. Whe the secondarys on the 1st carb start to open the primarys on the 2nd carb start. That gives you the shot of gas you need to get rid of the bog. Im still not proud of these carbs for street use. They were intended for a tunnel ram and drag racing where you come off the line at WOT. If I cant get mine dialed in right I'm gonna go with a set of 390 vacuum secondarys. As far as leaning out the rear cylinders, Im running a Blue Thunder intake and if you mount the carbs backwards the primarys on the 1st carb are right in the center of the engine. Of course this is an FE section and I'm running a small block in disguise.
