RingWinger,Try a Walbro WT 499 Carb,it is used on the Zenoah 23cc glow engine.cost around $50,the diaphragm is made from a different material and i do not beleive it will swell.I used to have to change the diaphragm material in my Briggs race engines when i switched to methanol.The stock diaphragn would swell on methanol,i wonder if you can use a WT 499 diaphragm in other Walbro carbs,that would be a cheap fix.