OK... So between a Carter and a Zenith, any questions on the potential replacement carburetor?
Just run regular gas if you want to; if you ever decide to change the carburetor I'd suggest a complete fuel system overhaul to include all NEW parts- gas tank, fuel lines, fuel filter, fittings, and carburetor. This will provide a control of sorts to help you make your own determination whether, or whether not, anything at all is going on with the fuel you are using. New parts are not the same as the "cleaning & clearing" from before. (yes, I just re-read all eight pages you linked to)
Drive it & run it often!
That is my opinion on how to make every type of engine happy.
Brad
