Main jet sounds good for 78 is about par for the 217 atomizer (you could try a 77 jet and or or different needle clip selections) but you need to dremel open intake hole on cylinder to around 16mm,
notch piston skirt for full open intake @ tdc, sand or mill the head head ring and tabs flat, base space cylinder at least 1.5 mm bevel piston sides a bit more for full open transfers @ bottom dead center, 18 degree timing
Do this and your carb settings will probably match better and you will hit about 40mph
With the mods I just said but with stock 12mm carb and stock pipe with just a 5/16 hole added to inside and end cap I get 35-40 mph with my 200 lb