Manual says: "The ignition module is set not to operate below 120 rpm for safety."
In my case the prop position around 1 o'clock helps to hand crank more easily. It is very tricky but it might affect to speed-up rpm.
Also someone above mentioned rich needle set affect back-fire.
With your helps to tight exhaust maniffold with Nord-Lock washer no more manifold leaks, and much easy to hand-crank right.
Getting colder here. Good Luck