ERIK, I don't think you ae going to find many guys that even know "Merco" engines were made at one time, much less know the diameter of the carburetor base. What you have to do is measure ,or have measured the base, in mm or inch decimal fractions, and ask who has one of the same size. A brand named "Perry" is a good one to look for. I have a half dozen but can not help you without knowing the diameter. Luck, Eloy