Inside the carb are two settings. ONE: is the float level. The seam of the float should be level with the main body of the carb. There is another method that has advantages especially for older floats, that is measuring the level of the fuel. The second stting inside the carbs is the needle height. TWO: needle is set on second notch.
Those are generally the only things inside the carbs you mess with. There's one other thing that was attended to when the carbs were rebuilt, that is the fit of the butterfly in the throat. So you set the butterfly when you changed the O-ring and you set the needle on the second step. The only thing you should have any business messing with is the float adjustment.
Try some starting fluid as Bill suggests. I know, I know, I don't like it on principle either but it sometimes helps.
I checked the Bing book. The idle mixture screw is 1 turn out for initial setting. It may help to get this monster running to have them a little rich, even 1 and 1/2.
After it starts and runs for a couple of mins one of the first things to check is timing for full advance with a timing light. And check idle at about 1000 rpm, full advance 3000 rpm. If the timing is off it will be hard to start.
I just brought my bike home. I have to go back now and get the car. Bike had a broken wire in the harness for the booster. I was changing the points when I found the broken wire. I had the timing light with me but it ran good enough for the 4 miles home. Will check timing later and put the cover back on before I go to Laural, Md. Tomorrow.