Can't tell if I'm running too rich or too lean

The flame out would appear to be as you close the throttle which is when you get maximum vacum

1. do you have a vacum petcock - if so switch to the prime position and clamp off the vacum hose
2. Is there gas in the air box
3. Do you have Emission air bleeds to the exhaust through the cam cover - if so is it drawing gas into the exhaust from the airbox

Just a couple of things worth checking as you appear to be getting raw gas in the exhaust, if this flame out was coming from the combustion chambers I would expect more "popping and banging" than there appears to be
PS: you might want to ease up on the flameouts in the garage if the airbox is full of gas 

There's some gas in the airbox, which means my carbs are still overflowing somehow. The rest of that is a negative though. I have the vacuum petcock currently plugged and the associated port on the carb plugged as well. I have it in prime mode pretty much always now.

Nessism wrote:

Are you sure the engine is running on all four cylinders?  You might want to start up the bike from cold, then check the header pipe temperature to see if there are any dead cylinders.

having only checked with my hands, every cylinder is hot, I have also confirmed spark on all four.