Tight Timing Chain

[Roscoe]

what I'd probably do,.... run it a few minutes by spraying carb cleaner in into the carb. Or gas from a squeeze bottle, ... or a temp gas tank gravity feed to the carb (like from an old mower)... or plug the vacuum from the manifold and use a different vacuum source to cause the petcock to stay open. I'm thinking you need to run this thing a while and let it loosen up or break so you can ID the problem and fix it.
Stay after it, we'll get it going or find the reason why it won't.