Sir, you definitely have a fuel delivery problem or it could be the fuel air mixture screws are not set accordingly. For troubleshooting purposes, set the fuel air mixture screws (this is the brass screw with a spring on it on top of each carb) to two turns out from lightly seated. As soon as you get the motor to run, you can reset them later. Remember, from lightly seated meaning you will turn each screw all the way in while ensuring you ease in before hitting bottom. Even better unscrew each one all the way out first to check it is not damaged, meaning it is evenly pointed. While out, spray in some carb cleaner in each hole. Then re-screw each all the way in easing just before bottoming out to prevent damaging the points. From there, unscrew each two turns out.
Next, remove the air covers on each carb. Get a spray bottle (even a clean used glass bottle sprayer will do) and fill it half way with fuel oil mixture from your tank. Get another person to do the starting and cranking. Do the test run again, making sure cooling water is provided accordingly. Stand infront of the motor with the spray bottle while directing the other person to do the starting. Make sure he engages the choke (push in the ignition sw and keep pushing while starting) If the motor coughs, like I saw in the video, stop the choking for the next round of starting. Instead, as soon as it starts coughing or running, start spraying fuel oil mix into each carb while listening for changes in engine rpm. You need to find out which carb when you spray into it increases rpm. This will tell you which carb is not getting enough fuel. From there you can start troubleshooting, especially with the float position or even with a sticky needle.
The other thing to check is to make sure the carb's throttles (not the butterflies at the front but instead those way back at the "throat" of the carbs. You will need a flashlight to look into the bore of the carb's to see this). are slightly open in their idle position. If not adjust the idle accordingly. And this is the idle screw at the bottom of the control tower.
At the same time, while you are able to run the motor with a fuel spray, monitor the clear fuel filter. Report your findings on your next post. Goodluck.