All of the testing is done in neutral in the garage, since I don't want to risk the bike stranding me and having to push it back. So it's not only under load.
I didn't verify the float valve height, but there wasn't any reason for me to suspect as much. Tab didn't look bent in any way. Jets are the correct 115 Front and 112.5 Rear for the solenoid carbs. Needles are stock with the spacers in the correct order. Diaphragms are also intact, with no light passing through the membrane. PMS screws were stock since I had to drill out the caps, but are currently set at 2 turns out, and I've played with up to 3 turns out. Based on the internals, It doesn't appear that anyone had gone through and messed with the carb internals. Though I could try running with the exhaust pipes off since they were off when I got the bike.
Tank isn't a problem since I was running an auxiliary fuel bottle with fresh gas directly into the line that feeds the fuel pump. Fuel pump is working because I can hear the clicking and Ive accidentally run it when the lines weren't connected to the carbs. I've also gotten the same results with the tank connected, which was also drain and fresh fuel put in. Needles and seats look good, with the conical rubber looking fine. I get no fuel leaking out the vents or overflow.
I've also eliminated any strangeness with the solenoid passages by removing the o ring on the main jet that seats with the fuel bowl.
I'm not opposed to ruling out the obvious again, since I'm kind of at a loss and it's good to be double checked. At this point I have cleaned the carbs in some manner 3-4 times, once entirely apart with the carb bodies soaking in the ultrasonic cleaner, same with the jets. As mentioned earlier, I check for light passing through the holes and used thin carb cleaner wires to make sure nothing stubborn was in there and blewout all passages with compressed air.
Since I can use an auxiliary fuel bottle, I might try to rule out the fuel filter by disconnecting it entirely.
As for intake leaks, I've run the bike in nearly every intake configuration (because I started to lose my mind): carbs only, intake elbows, air box, air box to cleaner connector, half of the cleaner, cleaner with no filter, cleaner with filter. Obviously things didn't run right, but I was trying to see if anything could be gleaned from doing all of that. Gaskets between the air box and air cleaner halves are still there.
The things I haven't done, based on reading all of this, are checking for float height, ruling out the fuel filter, ruling out the TPS (would need to check that resistances are in spec), and checking compression.
I also had another thought about checking for intake leaks. I've generally used aerosol carb cleaner, but I've read about people using propane gas to test for intake leaks. Would the gas be able to better penetrate thin cracks versus the carb cleaner? The only reason I ask, and one of the things I suspect, are the engine side intake boots. They have cracks on the exterior, but I don't see any cracking on the inside, and spraying carb cleaner at them while the bike is idling doesn't produce a change in the rpms.
I'm in northern Alabama, so I'm a bit far from you patrick, though the offer is immensely appreciated. I'm also going to be out of town for a couple weeks soon, so I won't be able to try much else. Certainly don't have time to throw new parts at it. I would love to find someone who would let me put their known good carb in, since that could rule out that chunk out.
This is the most puzzling carb I've dealt with, and I've worked on quite a few, including an 03 vstar 650. I'm just thankful that it's easier to remove than a v65 sabre's carb