won't idle below 1000rpm after rod and jet change

NO. A properly setup carb, the idle mixtures will "peak" at vacuum AND RPM with the mixture the "engine likes." More lean, RPM and vacuum falls off, as does too rich.

Before we had "smog carbs" with leaner idle circuits, many carbs could be richened up so much with the idle screws, that the engine would die.

I still say...............You have a vacuum leak

And from the looks of that plug, it is NOT running rich