Green’s Dictionary of Slang

(US) a two-cylinder John Deere tractor of the 1930s .

1957		‘Weldon Hill’ (con. WWII) Onionhead (1958) 11: So Al drove the big Popping Johnnies around [...] the flat sprawling fields.
1996		J.C. Truett (ref. to 1940s)Circling Back ix: [I]n the 1940s [he] climbed on board a two-cylinder “Poppin' Johnny” Deere tractor rather than his sorrel horses.
2008		M.C. Blew Jackalope Dreams 134: An old man [...] on a little John Deere tractor, the old poppin' Johnny model with a mower blade attached.
2019		https://docarnett.com 14 Feb. 🌐 The whomp-whomp-whomp of single-cylinder engines almost always makes me think of Roy Morris and his old ‘Poppin’ Johnny.’ Those of you with rural roots probably know that refers to a two-cylinder John Deere tractor.