Regarding how the ignition retards for start up, as you flip the prop briskly during start, the ignition senses the speed of rotation as the magnet passes under the sensor. If turned fast enough, the ignition will retard the spark. If turned very slowly, the spark will not retard. Some people get a kick back when using a limp wristed flip because there is not enough rotation speed to create the retard. These ignitions should be called auto retard rather than auto advance as they can never advance the timing beyond the preset static timing. Some time in the past they were called auto advance and it stuck with them.

Some years ago, I bought a used Brison 2.4 that would pop and run a bit but not well. I could never find a definite problem why that engine would not run right until I disassembled it. I found that both of the main crank bearings had the seals blown out causing a severe leak that suppressed the crankcase compression / bypass. No trace of this could be seen w/o removing the crank. When you rotate the engine, do you hear the normal bypass airflow through the cylinder intake ports? Do you have a muffler in place? Some of these old chainsaw based engines won't run well at all w/o some form of muffler or pipe in place.