TOPIC:

Are you still using the vacuum operated tank shut off valve?

You've got an interesting problem. All carbs I rebuild whether bought on spec, or from folks like yourself are set-up on my bike and road tested.
2 concerns: 1) The problem existed prior to my work on them. There were no problems setting them up and no issues with the road-test. (Nothing goes out the door unless it works !) Glad to hear you haven't "monkeyed" with them. That eliminates many potential concerns. Lets assume for the moment that they didn't fall off the mail truck and caused an issue with the float levels.....which I will guess by now, you've confirmed !
When I don't hear the gurgle of the bowls filling up I know its not going to start. I leave the gas on and come back an hour later. When it starts it will run like crap for a few seconds until the other bowls fill up and the cylinders start getting fuel. They do, but there is a delay.
This is the 2nd concern. I've had many different sets of carbs on my bike for final adjustments and EVERY one of them have "gurgled" when the fuel is turned on and the bowls fill. No exceptions. So... I'm still confused about : "leaving the fuel valve on and coming back an hour later, it starts but runs like crap until the "other?" bowls fill ? This is illogical !
At this point I can only suggest you've got a serious issue with your fuel-line/filter arrangement.
At this juncture it would be very helpful if you could take some pictures of your fuel-line routing ? With and without the tank, so we can see if there's something obvious.

kawboy asked about a "Vacuum operated fuel-valve". That could be the problem !!!! Thanks

how does it start and run if you leave the gas cap open (maybe the tank vent is blocked)

I've tried leaving the gas cap open, it has no effect. It is the factory gas cap. Sometimes it will weep a little gas through the keyhole if full. I'm not sure if that is relevant.

The stock tap has been long since replaced with a pingel. It my second pingle, the first one leaked around the valve and was replaced by the company.

My gas line runs directly out of the back, facing the space between the cylinders. Does a sweeping curve over the top of the motor on the right hand side, where the clear filter is located, up over the carbs and down to the nipple. No kinks. When the line is taken off the carb, fuel POURS out the end. This I did check multiple times. I have a Hayabusa that had an intermittent fuel starvation issue. The line would kink slightly when the tank was lowered down, just enough to restrict the fuel. I replaced the line, checked the routing and problem solved.

This problem existed before the carbs were rebuilt, in addition to their many other issues. I was hoping the rebuild would solve it but it didn't, so I doubt it was the carbs. New lines, two new filters of different designs, two new fuel taps.

Scotch, when I say it runs like crap until the other bowls fill up is just a supposition on my part. That may not be what is happening. Bike will start, runs rough on less than 6 cylinders but within seconds, say 20 or less, the others will start to fire and it smooths out and runs on all 6. When it does this, I watch the fuel flowing through the filter and I can clearly see the volume of fuel is reduced until it is running on all six and I can see the flow increase through the glass.

On occasion, I have seen it fire right up, starve for fuel 30 seconds later, run like ass, then normal operation returns with corresponding fuel flow. During the rough period I can see the fuel is not flowing.

First thing I will do is re-investigate the vent line. Last time I checked I used a guitar string to push through the passage and also blew air through it. it didn't solve my problem then, but my carbs were crap at the time so perhaps it has since plugged and the other carb issues covered it up as I chased them around.

I do not have a hose on the bottom nipple of the tank. It never had one and I've never seen fuel come out of it.

Of course I can't even run the thing atm the with the defective solenoid so I need to solve that issue first. Is there a source for an acceptable alternative if OEM is unavailable, which I assume its not. I took it apart again. I can't find anything wrong with it unless the windings in the bottom are compromised, or the little wires that are supposed to touch it, aren't doing so in the correct manner. They are so thin and tiny. I am going to replace them with a heavier gauge wire so they don't bend trying to get them through the tiny holes provided. All I know is it tests fine going in, but power does not come out the other side. If I jump the terminals the starter will spin no problem.

So I'm wondering if your float needles are Viton tipped? Could it be that the needles are getting stuck in the needle seats in a closed position and then once it fires up, the vibration from the engine loosens up the stuck needles and the fuel starts to flow.
'Just throwing it out there for consideration. I can't imagine any other reason for the fuel to trickle until it finally gets running and then things are fine.

I don't know the answer to that question as Scotch did my carb rebuild. I can only assume he used what was best.