At 4000 RPM are the secondaries even open? I would still plug the secondary PV and jet up. Put an 8.5 PV in the primary, if it still appears flat try a 9.5. It needs to open when the load is high enough to warrant the extra fuel. And don't worry about any effect on idle, the idle jet is much smaller than the main jets feeding them. As far as the sputtering at 1600, have someone hold it there and cover one of the idle air bleeds, if it gets better try covering two. That would tell you the IAB/IJ sizes are too lean for the transition circuit and need to be changed to enrich the circuit. If it gets worse, then it is too rich. As far as the idle, pull the carb now that the idle speed is set and see how much of the transition slot is showing. should have roughly .020 exposed with the blade set for the correct idle speed. What kind of timing curve do you have? Insufficient initial timing will make tuning harder and will run poor, with that much cam I would expect a minimum of 20˚ initial, and maybe up to 25˚