Set a piece of paper on the throttle screw see if it's tight, maybe the blades are sticking from a bad cable, you probably checked this already but something is causing this other than the stuff you swapped

PS: on a side note, a weird place for an intake leak, but possible is a damaged valve guide and seal some air can be sucked trough the crankcase vents, in this case it should be burning oil.

 

Throttle cables are as new. I checked the valve guides and replaced the valve seals when I rebuilt the heads earlier this year. It doesn't seem to be burning any oil.

 

This is the first thing that comes to mind. If you are not running lean it is possible that you have an air leak.