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There can be air passages that need cleaning in the carburetor body. Sometimes they need reaming with a finger driven drill bit. Often the adjustable idle circuit is an air adjustment, not fuel. The gas engine can run rich from external influences, like a dirty air cleaner, a choke not opening all the way, and from internal things like a leaking float needle valve, a leaking float, or a maladjusted float, all causing a high fuel level. You can adjust the mixture by changing the float level, you need to do that for some speeds. To quote one nearby shop man, "If you haven't replaced the float needle and seat..." he didn't have anything that he'd tell me. He said after I replaced those if I still had a problem he'd talk. I did replace needle and seat (had them in my hand that day) along with plugs, plug wires, reattached the choke cable sheath, changed the dome on top the precleaner (JD-4020) to be up instead of smashed down, cleaned the air cleaner, removed junk from the manifold and then I didn't need to adjust the carburetor. It was fine and I cut fuel consumption significantly. Adjustments can seem to not make an effect if you try to adjust idle mixture at higher speed and try to adjust the high speed jet at idle speed. They do interact and the governor works to hide the affects of those adjustments. When adjusting the idle mixture with the engine idling as slow as the governor will allow you can often see the effect of that adjustment by looking at the throttle arm. It will move while maintaining the same engine speed, and you get the best results with the throttle closed the most for the same idling speed. I adjust the high speed jet on my MF-135 while plowing in a higher gear for fastest plowing speed, though that tends to be a bit rich, but I'm getting the maximum horsepower. Adjusting it at high speed without a load isn't very productive. Gerald J.
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