running on full choke usually indicates gummed up carb. and maybe vacuum leak caused by loose screws on the carb. or cracked fuel line/ primer bulb (not likely beings it's not that old). If it has set with Corn gas most likely the carb. passages are almost gummed closed. I would drain and clean the fuel tank and in tank filter, put fresh gas in it and run some additive through it beings it does run. maybe that will remove some of the varnish.

Carb. adjustment tools are available online. First you have to idenify what type of splines the hi and low have. even on some carb. they have limited adjustment so you may not be able to turn them vary far without removing the limiters. I think the carb. is dirty and if you get it cleaned up it will run fine by the way you describe the problem IMO.