tkg,on some carbs all you need is to hog out the needle area (no welch plug), direct feed from under the diaphragm to needle and very large orifice to the venturi.

Jack,I agree the wb-25 is a poor choice for the 100cc class engine. I bet if you bought enough carbs from Walbro they would taylor one to your specific engine, or you could just pay to have them do that.