I have this engine and it runs good on gas with the stock mufllers.
swings a 20x10 prop. When it sets for a long time I prime it with a
squirt of gas in the carb or use the choke and spin it a few more times. On gas you have to spin it fast for the ignition to have a good spark so it will start. Hand propping will not work. Use a starter or the pull start option on some engines.