[mongocanfly]

Yeah...its one solution...but may not fix it...
I copied this...

Dieseling is a common problem, especially in warm weather or when the engine is hot. In this case, it is usually caused by running "cheap" gas with inadequate octane. In this case it can usually be remedied by switching to a higher octane fuel.

In milder street engines, another big cause for engine run-on is having the idle set too high, or the carb is misadjusted which requires the idle speed screw to be screwed-in too far to allow the engine to idle. When the idle screw is screwed-in too far, it opens the throttle plates too wide and actually pulls fuel through the main jets a little, so when you shut the engine off, the inertia of the spinning engine still pulls air (and some fuel) through the carb and into the cylinders and the heat built-up inside the combustion chambers is enough to light a few of the cylinders at random to keep the engine spinning and sputtering. Again, this is especially true with fuel that isn't high enough in octane. The more the octane, the less volatile the fuel. Even though the key is off, the engine won't stop sputtering because the throttle plates are opened up enough to still pass a little fuel and air

Fuel injected cars don't have any Dieseling or run-on problems because the fuel is electronically pushed to the injectors via an electric fuel pump, and the injectors electronically fire, so with the key off, the fuel delivery completely stops. Carburetors aren't electric, so even when you shut off the ignition, the inertia of the engine still rotating is still sucking-in a little air and fuel, and as long as it is still rotating