Greetings Eric - nice bike!!

When you say "stumble/missing off idle" I assume you mean it idles well, but from idle to 1/4 throttle it isn't smooth.

As long as you are certain that the tappet clearance; points gap; and timing are perfect.....

What needle clip position are you in? (IIRC #3 is standard for most elevations.) Tried varying that? While you're at it, make sure that the needle doesn't have any slight bends in it and that it is super-clean & smooth. It should provide a smooth and perfect seal with the needle jet.

Good luck!

- Dan