Try testing with a new plug. I had JD do that. The customer ran the engine with the choke on and ruined the plugs. New plugs and it ran fine after I retrained him on how to use the choke.
Next, would be to check the "trigger" if it is a Kawasaki engine.
If Briggs or Tecumseh engine, check with kill wire disconnected. If still has condensor, check points and condensor. Could be bad magnetto(coil).
If Kohler engine, check points and coil.