You pic didn't post showing off the plugs which would help.
I'm assuming you took the carbs apart and made sure the float height is all the same? If so you may have to take the carbs out and take a look at number 3 carb, it could be gummed up with rust flecks or varnish. Take the pilot and mainjet right out of there soak them in brake cleaner then take a small wire and work it through the hole in the jet. Make sure there is no crud under the needle valve stopping the fuel prematurely and starving that carb. That cylinder is obviously leaner than the others at idle and leaner than the rest. You can hear it slightly at idle and the other cylinders which are perfect can't totally mask the lazy cylinder. Also when you rev it and it hits that cylinder you can hear that it kind of skip a bit then accelerates. The other cylinders sound awsome. If you recheck the mixture screws on that cylinder I'm sure it will clear it up. Make %100 sure that it's set to what the other cylinders are. If you are %100 sure, turn the mixture screws a 1/4 turn at a time out until the cylinder has enough juice to be in line with the others. That cylinder is also causing the idle to hang up a bit when lightly revved.
Here's what to test before taking the carbs off:
(Can skip this step if you're sure of the float height)
If you want to see if that number 3's float height is jiving with the others you can do it without taking the carbs off. Get some clear plastic hose and attach it to the drain nipples on number 3 and number 4 on the right hand side of the bike. Curve the hoses to be above the float bowl and temporarily tape it to the right side of the carb bank. Open up the drain screws and the fuel should fill up the hose dictated by the float height. Take a look. Sometimes even when the float height is set to say 14.7mm or whatever for the gen1 there will be minute differences. If there are air bubbles just start the bike and they'll go away. Are the levels within a mm or so of each other?
Here a video where he loved it so much he made it permanant which I think is overkill:
http://www.youtube.com/watch?v=OG1Qiki7hH8Another test you can try is turn the mixture screw on that cylinder a full or half turn out temporarily then measure the temp of the pipe in case you miscounted the turns out or turned it the wrong way. I've done that before, So for example, you have it at 2 1/4 turns and not 3 1/4 turns so the cylinder is dragging and getting even leaner. Is it now falling in line with the other cylinders? You can compensate for a gummy pilot a bit by opening the screws on that specific cylinder. It's also not unheard of to have a cylinder needing an extra 1/4 turn or so more or less then the other cylinders. Since every carb has microscopic machining differences, amounts of wear on needle valves, etc some may need more or less. What does the plug look like? Try riding around in the "dead zone" and pull that plug with some gloves or wait until the bike is cool. If the base ring doesn't have at least one full turn of colour you're running lean on the pilot on that cylinder. Recount the turns on that mixture screw to be sure it's in line. Maybe you leaned it instead of riched it up when adjusting to 3 1/4 turns by accident? I've done that before too having a brain fart and turned it the wrong way. If you turned it the wrong way by accident that cylinder may be 3/4 of a turn IN from 2.5 which would make it 1 3/4! Instead of 3 1/4. Reset that mixture screw!
Here's a tip which helps so you don't have to pull the carbs to reset the inner carb mixture screws. Get a flathead bit that is a few inches long such as one for a multibit screwdriver. Turn the mixture screws in which if your on the right hand side of the bike for number 3 carb to the right or towards the engine block until it's LIGHTLY seated then take a cheap dollar store dental mirror or ransack your wife's purse for a hand mirror and with a magic marker mark where the mixture screw has stopped on the underside stalk ring. Use the hand mirror to make sure your marking it correctly. If you're off just wipe it off with your finger and try again.
Once it's pretty good insert the screwdriver bit like your going to unscrew the mixture screws and make a mark on the outside of the stalk and continue down onto the driver bit. Now when you turn the turns out as long as that line comes around and you can see it from the outside it will be one turn so you don't have to micromanage with a mirror to count. So now just unscrew and when the two lines on the outside of the mixture screw stalk and the driver bit line up it's one turn. So count out 3 turns, then get the mirror out and turn another 1/4 turn to be in line with the others. Retest the bike. Once it's pretty well spot on you can use the tiny 3/4 inch flathead bits instead of the big momma to fine tune.
