the reason i dont use a disc coulter is simple, i dont have one as for the adjustments there's the handle on the top of the plough for depth and a swivel point on the hitch part for leveling it. and the 3 holes in the hitch of course
those kind of "carbs" are pretty widely used on small ic engines as they are pretty simple to make, i have toyed aroud with building one but never got round to it
i believe there are replacement carburetors readely available on ebay for not that much, briggs 3 bolt carb i think it is?
http://www.ebay.com/itm/398202-Main-Jet-Nozzle-Carb-Briggs-7-9-HP-Emulsion-Tube-2-Pc-Flo-Jet-OEM-New-/151840308366?hash=item235a633c8e:g:BGsAAOSwAodWE935
i've done three competitions without them, for not using them i dont think it looks all that bad. theyve told me that if you have to look back, stop, let go of the steeringwheel and then look back