Small Engines (Lawn Mowers, etc.): Ignition, cold start, model numbers

Question
Mower will start Quickly on cold start and run well. When I shut it off, It will not start again. It will turn over and grind , but it seems there is no spark. If I wait til the next morning, it will start up. Is this the ignition unit before the spark plug gone bad? If so , what is the part and where can I get it?

Answer
It could be an ignition problem as well as it may be valve related,
but for me to give much help, I need to know what brand engine, and
what the model numbers are, so if you can locate the numbers, model/serial, etc., that would be great.

Thanks,

Fish