its all depends on the gearing but 20 to 30 most likey 3.5 is kind of small 5 hp briggs and right gears 70 you can type
how to build a go kart
or type into search box briggs 5 hp
go kart parts even look into kart racing forums really you shoul dlook into getting a bigger motor 3.5 wouldnt be big enough does not or wil lnot have much power or speed