I have a toro 2 cycle lawnmower. When I start it cold, it starts on the first pull. After running for a few minutes and the engine is hot if I turn it off I can not restart it. If I let it sit for 20 minutes and it is cold again, it will once again start on the first pull. A friend told me he thought the magneto/ flywheel assembly needed to be replaced. How about a second opinion?