Teach , What is the condition and age of the Spark Plug , is it firing ( bright blue ) spark or dull yellow and is it clean or dark and carboned up . I would suggest a new plug if yours is suspect or more than a few yrs old. If you have confirmed optimum spark then fuel starvation is the secondary root cause . You will have to ensure that the fuel circuits & inlet needle valve under the float are confirmed clean via tag wire , compressed air and carb cleaner usage . Add 1 ounce of cleaner to your fresh fuel after you have clean carb as advised. P.S. The obvious proper oil levels and clean air filter apply also . Let us know how it goes . I would rule out a defective coil since 10 seconds is not sufficient to heat up this unit .

The spark plug is very clean and firing. What is a fuel circuit & inletlet needle ?

Very small orifice (holes) within the venturi (throat) of the carb and also within the carb float bowl area . The inlet needle valve is a spring loaded (moves) metering valve right under the axisis (pivot) point area under the float . It allows fuel to be drawn into the carb circuits once the proper fuel level is achieved . Concentrated Fuel Carb cleaner 1-2 ounces within fresh fuel may start the cleaning process overnight if your carb has not excessively restricted give it a try 1st and let us know if unit starts and continues to run well one warmed up ..