What causes a riding lawn mower to spit fire and black smoke through the exhaust?

Question

Thank you for your help!

Answer 1

The cause is that it's broke.

Answer 2

Two things will cause this, ignition timing or a burned/sticking exhaust valve. The fire is from the valve being open during combustion and the black smoke is unburned fuel caused by the valve being open lowering the compression. If you hit something with the blade recently you may have sheared the key between the flywheel and the crankshaft. This is the easy one to fix. The engine cowling and flywheel will have to be removed to replace the key. The burned/sticking valve may be a bit harder. If the valve is burned the engine will have to be partially disassembled. Not knowing the model of the engine your talking about it is hard to describe the procedure.

Answer 3

Does it do this constantly or after it warms up? It sounds to me like its running too rich. If the carburator has an adjustment screw on the bottom of the float bowl, try this:
with it off and cool, turn the fuel mix screw all the way in till lightly bottomed. Then adjust out 1 1/2 turns. Start the tractor, itll run rough , but itll run long enough to adjust it. Turn the fuel mix screw out till it starts coughing/sputtering. Adjust it back in till it smooths out.
If theres no adjustment screw, then im afraid the carb will need a thourough cleaning.
Id change the spark plug while adjusting/cleaning the carb as well, specially if it hasnt been changed inna while.
Kidd

Answer 4

No but when i was in high school there was a kid who rode a small john deer mower to school and proceeded to take it down main street when school got out.

Answer 5

Your lawn mower needs an exorcist

Answer 6

You may have gotten some water in the oil or gas.