I know what u mean by sore arm. I did same on my first run of my 50cc on my P-40. Arm was so sore i could barely hold my coffee cup.
My friend gave me two starters - one for small and one monster for my 50cc. I picked up a Jump Starter with air compressor, light, usb plug, 12vdc cig jack, and jumper cables. Works great. Starts right up each time and like yours i can flip it once to start if it has been running.
Glad your engine is purring!!
Keith