Can you hear LP flowing internally?? Like a tire hiss?
I wouldn't recommend it unless you are really careful, but I've hand fed lp into the carb before and started them that way... At least that gives you more knowledge on exactly how much fuel its getting.
Or you might whisper just a touch of ether into the carb while turning it over and see if it fires or tries to take hold. If it backfires, you probably have the timing off or a wire or two wrong...
I've seen all sorts of quirky starting engines - one of my old MMs you had to take the natural gas feeder line off and let it pull fresh air briefly then start hand feeding fuel. It would then start easy and run like a sewing machine, but it wouldn't start for anything until you did that.
Dad also has an old HUA MM that you HAVE to primer it with a little gasoline before it will start.
I don't remember an M6 regulator specifically, but quite a few of them have a spring loaded button in the middle that you press to flood a little extra fuel to the engine.