Jim, I take the easy/lazy way. I simply order a replacement carb for a like displacement engine from an R/C engine vendor. Example, a couple of months ago I bought an airplane with a 3W 70 twin. Even after rebuilding the original Tillotson carb I still could not get it to work correctly. I ordered up a DA 70 twin Walbro replacement directly from DA. Works like a charm and since I ordered it from DA I know I got a genuine Walbro carb and not a knock off.