H running rich

Where to start. I adjusted just about everything I can and the tractor idles rich. On a pull, it runs great but when idling or very slow it is rich. Any suggestions welcome Thanks Henry

The carb Idle mix screw works backwards, Out is lean in is rich, it is an air bleed, not a fuel valve. If this does not help, The float level might be too high, allowing fuel to enter the engine through the high speed passages. Good luck. Jim

Jim is correct, here"s my complete "H" carb tuning procedure;

Make sure the float isn’t sticking or touching the insides of the float chamber. Some previous advice was to use a Dremel tool and smooth the insides of the float chamber so it doesn’t rub or touch. Pretty important. Set the float so the top of it rests 1 27/32" above the flat surface of the float chamber.
Initial settings are as follows to get it started;
Main fuel adjusting screw, big screw facing down at an angle, towards the rear, at the bottom of the carb; 2 1/2 to 3 turns open. This main screw turns clock-wise for leaner mixture.
Idle fuel-mixture screw, smaller screw facing forwards, on upper left-hand side of carb; 1 to 1 1/2 turns open. This idle screw turns counter-clockwise for leaner.
Idle speed screw, faces outboard, at the top of the carb; set for 450 rpm, and make sure the governor correctly engages the slot.
Final settings are determined as follows;
Get the engine warmed up, and idling.
Turn OUT the idle fuel-mixture screw until rough running, then turn in until it idles smooth. (Mine is set at 1 turn open.)
Rev it up, wide open, warmed up, then turn the main fuel adjusting screw IN until rough, then out til smooth, then 1/4 turn to 1/2 turn further out. (Mine sits at 1 turn open. Other advice has been to set it at 2 1/2 turns open for pulling implements.)
Should rev up smoothly and evenly.
Too Lean = stumble, sputter, damaged melted plugs.
Correct = tan plugs.
Too Rich = back smoke, black sooty plugs.

Mine was that way, had bad plug wires. It will NEED a richer mixture if the ignition is not right. Make sure you have good blue spark to all cylinders and timing is right.

You might be surprised that it will run leaner.