had a phone call about this thread, so thought I'd chime in.....some of this is in my white papers, some not....some good advice so far, but from the sounds of it, the OP's problem is likely inconsistent intake heat. Big plenum with 800cfm on this combo is a combo for no velocity/ no main circuit actuation. Making sure the intake is warm helps. If you can a 4 hole spacer would likely help. The blue spring is likely wrong and could be some of the problem, see white paper on afb's for checking procedure. i would bet a yellow spring is what you want. The 800 is not too big, but they can be a little trickier than the 750 to make work on this type of combo. Leaving, then bogging, then going is a sign of the pump shot being used up too early. the proper springs will help, pump arm in the furthest hole inboard will help. go back to stock jetting , that should work fine.....depending on altitude, 110 front, 107 rear may be optimum. Raising pressure may help, this is not an across the board fix, it made sense for old irons combo. You may want to try adding 1/2-1 lb. be careful as too much will unseat the needles at idle. Old iron, the reason for the top end dying is a result of the increased pressure/ braking force....causes fuel to spill from bowls thru the secondary boosters. several options...dont slow down so fast, try lowering pressure a bit at a time to find a happy medium, or if you have a boost referenced regulator hook the vacuum port to manifold vacuum, this will pull pressure back at idle/ high vacuum. As already mentioned, drilling the weights will make the problem worse as the secondaries will come in sooner. There is an inherent problem with two of the internal circuits in these carbs that actually causes the exact issue , this is one of the things i address on my custom carbs, but you can make stock ones work following these directions.