If your light throttle cruise mixture is that lean, why not try opening up the main jet a little? Until the power valve opens up, all the fuel has to pass through the main jet, so that's where the idle system is getting its fuel. That deep dip just off idle makes me think the accelerator pump is not doing its job, also. If you can mitigate the stumble by using a bit of choke, that would also point an accusing finger at the pump. Final suggestion- - - -try dialing in a couple of degrees more initial spark advance. A late timing stumble is almost identical to a lean one. Together, they really make performance suck like a Dyson vacuum cleaner!
Jerry
