[olddog]

When it first fires, it sounds like all cylinders are hitting. In the video, you never pulled the throttle while it was running. It acted like the idle was set too low and it was going lean.

You pump it and squirt gas in. When it starts there is enough fuel. After it runs a couple seconds, it goes lean and dies.

If you don't think it could be too lean, then I would suggest you loosen all the valves a quarter turn (make it 1/2 turn for hydraulic lifter). That may be too loose, but it will tell you if you have them too tight. It's a quick test.