Super comprehensive check and do list, it WILL start! By golly gee willakers! No matter who's bike; unless ya got dirty carburetors or bad/dirty pilot jets set them 2.5 turns out, that is your friend to start with; pun intended. ;D
I re-watched your video; to look for any thing that didn't obviously stick out; I was just looking over the first time not really listening until you tried turning it over. This time around and help from a picture; I noticed you don't have the vacuum lines connected to the carburetor, even though the petcock will flow with out them on prime, they do need to be attached or plugged...it's the same as having leaky intake boots.
Also; if I am not mistaken you are using a battery charger to crank it over; unless your charger has a switch that has a jumper setting; you are not going to get but only 2 to 5 amps out of it unless it has an amp setting switch those usually only go up to 10 amps, which is not enough cranking amps, it will turn the starter no doubt about that, but not quickly nor strongly enough.
I have a car battery I keep around for jumping, testing bulbs, running a trolling motor sometimes etc. when you crank hold the starter and count 5 seconds, also give 5 seconds of rest in between, yank plugs immediately after cranking and see if they are wet; just to rule out any possibility fuel is not getting there properly, go ahead and bump the starter while they are out to prevent hydro-lock, might as well toss an ounce of oil in the cylinders to boost the compression and protect the cylinders and rings too.
Gas smells bad; bad gas smells even worse(Diesel is my preference, well fumes anyways), gas starts separating and going bad in as little as 14 days, octane ratings matter use the best to prevent knock and other fuel issues. You get over 40 miles to the gallon and hold 2.8 gallons whats 50 cents in this case?
Alrighty, something I haven't asked but should have; have you checked the all of the fuses? They can look fine visually; but still be open, a meter set to ohms or a fuse tester is the only way to know for sure.
Another thing I didn't mention is the clutch switch; even though the bike should start in neutral with the stand down, a faulty clutch switch can send it the wrong signal and lock out the relay, it will still turn over just not start; so strap or tape the clutch closed. Sometimes that little tab is broken off of the clutch switch, so check it, if it is there clean the switch and contacts.
Clean the spark plug boots, and inspect them for breaks and cracks...if you find one replace them. Take the boots and off trim about a 1/8th to a 1/4 inch off of the coil wires and give the boots a good twist clock wise on the wires until they are good and tight, this won't rule out the coils etc, but it will help rule them out unless the coil wire is broken, or bad out of the box plugs. When you place the boots back on the plugs; listen for a metal on metal sound making sure the fit good and tight.
Please check and do those things, so we can rule out the simplest things...fortunately, your valves are adjusted and your cam timing is adjusted correctly now, fire out of the intake moving into the exhaust is proof of that, it's heading the right way if it's going to back fire. Your cam chain adjuster probably needs to be replaced with the newer type so it doesn't jump a tooth again, when you can get a chance.
If the above has been done and checked, not just mentally but physically.(I tried this once years ago with a tech line; they weren't very happy that I was mentally checking against what I had already done or tried.)
First; lets see if the starter clutch is doing it's job right.
Pull the stator cover and watch how the starter engages the fly wheel, turn it with a socket by hand first and watch the sprocket behind the flywheel and flywheel and feel the motor as you rotate it, look for separate movement of the flywheel and sprocket and feel for anything odd.
You can also test using the starter but it's hard to see and impossible to feel; if you use the starter and can't see have someone hold it and count 5 seconds, When the starter button is pressed: The starter should spin and it's sprocket engage the chain, the chain should spin; both the sprocket and fly wheel, keep watching as the starter is released, the starter sprocket should disengage.
If the sprocket and flywheel do not turn at the same time; or you can wiggle them, pull the fly wheel and look at the wood-ruff key, is it broken, bent or cracked? does it fit the groove tightly? If broken/bent/cracked/loose replace it. Go ahead and tighten down the starter clutch bolts, they can back out all by themselves.
Since we are here; it is good time to check the Ignition pickup coil near the stator; there are timing points on the flywheel that charges the coils causing them to fire at TDC. If the sprocket and flywheel don't move in unison; it will make the coil spark at the wrong time.
Look for any loose wires or bad contacts...remember the clutch switch up above? This process is what it locks out, the clutch switch goes through the starter relay and IC igniter to here. Since we are at the safety switch end and your down there; pull the side stand wires and check its connections and terminals for corrosion.
Okie dokie; if all that is good and no start; lets get deeper into the ignition wiring, I hope you have a voltage/ohm meter.
The ignition key switch sends 12V to the junction box fuse labeled; "IGN" the 12V then goes to the start switch. If the start switch is in the run position, the 12V will go to the the pick up coil and then to the ignition coils.
If you get 12V at every terminal of the ignition coils including the wire to the spark plug, then those connections from the switch all the way to the Ignition coils are good. The spark occurs when the IC Igniter grounds one of the 12V wires. So there is power at the spark plugs but the IC Igniter can be shut down. There are two switches that can disable the IC Igniter, the side stand switch and the clutch switch. The damage to them is usually obvious or they are unplugged.
To check the ignition coils, use an ohm meter to measure from the tab connection to the plug terminal. Should be about 15,000 ohms; if not that coil is bad.
Starter relay; if a click occurs, the contacts cannot move, this is usually one click not multiple clicks, multiple clicks are most times a low or discharged battery. The click is caused by an electromagnet arm which that gets stuck.
To test it to remove the cables from the "B" and "M" terminals on the relay. check for ohms across the contacts; it should read as an open circuit. Then turn on the ignition, the start switch, and press the start button. The ohm meter should read near zero. If not your starter relay is bad.
Tapping(not hitting) the starter relay with a screw driver handle sometimes frees it up. You can by pass this to start the bike;with the same tapping screw driver cross the connections with the blade; it will spark so don't let that surprise you.
Summary:
Crank for 5 seconds; let rest for 5 seconds between cranks, no more no less.
1. connect the vacuum lines
2. Crank using jumper cables off a battery not the charger.
3. Pull the plugs right after cranking both should be wet.
4. Check all of the fuses with an ohm meter.
5. Check the clutch switch at the handle bars...plugged in/not broken? secure the clutch lever closed.
6. clean and inspect the plug boots, any cracks/damage replace them, trim the coils wires 1/8 to a 1/4 and re-secure boots.
7. Starter clutch/flywheel/shaft key
8. Pick Up Coil(by stator)
9. Check for 12v on all terminals of the ignition coil
10. OHM test the coils
11. starter relay test, cross connect the terminals while starting with a screw driver to by pass.
No mentioned for all other no start issues: Bad ignition switch, bad starter switch, valves and timing up at the cams. Ruled out because starter spins, or you did this already correctly.
If you go through this whole list one by one and step by step; you will find the problem and it WILL start. If it doesn't; I guess I need to plan a road trip.