When I turn the key off, my 92 Honda Accord won't restart when warm. It will turn over just fine, then start to catch, then stumble and then fail to start at all until it cools. This happens only when the engine is warm and only in warm weather.My mechanic has no idea what it could be. Thanks.

Sounds like classic main relay failure, where the cold solder joints on the PCB expand and fail in warm weather. Replace the main relay and the problem should go away.