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Unless you are in the tropics or the southern summer, you need the carburetor heat on. That will help. You do have two adjustments on the carburetor, one is hard to get at when it has the fuel shut off solenoid on the high speed jet. Your main symptom is one of excess accelerator pump fuel. That can come from a bad accelerator diaphragm in a Marvel-Shebler carburetor or a worn brass pump in a Zenith Carburetor. The one screw that you see is the idle adjustment. There are two ways to adjust it. One is to hold the butterfly against the idle speed screw and then adjust the idle mixture for the fastest speed. The other is to let the governor hold the speed and adjust the mixture for the minimum throttle opening. I adjust the high speed jet (small adjustment screw in the outer end of the fuel shut off solenoid) for maximum power pulling a plow. That tends to get the mixture a bit rich. All mixture adjustments are a waste of effort if the rest off the system is messed up. When I got my gas 4020, it smoked like an IH diesel. The timing was set wrong, the plug wires were carbon and broken, the plugs were too cold, the choke wire wasn't opening the choke, there was junk in the intake manifold above the carburetor, the air filter element was dirty, and the lid of the Donaldson precleaner was pulled down acting as a choke. Oh yes, the float needle and seat was worn making the fuel level in the bowl high that made it run even richer. So I put in a new needle and seat and made sure the float didn't sink. I pushed the top dome of the precleaner back up. I put in a new air filter element (though your 4010 should have an oil bath air cleaner. I cleaned out the junk. I anchored the choke sheath near the carburetor so it would push the choke full open. I put in AC or Autolite plugs with the right heat range in place of the bad Champions with new copper plug wires soldered to the connectors. And I set the point gap and timing to the right JD owner's manual. I've not yet turned a screw on the carburetor mixture adjustments. It no longer smokes and I have to choke it for starts, even warm starts. Unfortunately the manifold is broken so I can't run heat which the manual wants up to about 90 F when not working hard and up to 70 while working hard. All these things cut my fuel consumption from 400 gallons a year to 250. Paid off practically instantly. Gerald J.
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