Sorry Maniac, But I don't think that will even be close.
I was thinking my pocket bikes run a 6 or 7tt to 68t with an 11" OD wheel.
So if you were running a 20" wheel you'd want to go 6t to 150t? sprocket.
Or run a jackshaft, on my tadpole, I was going to run a 49cc pocket bike motor with a reduction box to a jackshaft to a final drive chain to a nexus 3 speed hub to get the right gearing for a 20" wheel.