Re: What is the cause of an engine...
Excessively rich idle mixture would cause cranky starting when warmed but would make for a great-starting cold motor.
Could also be ign problems, failing when warm. When it acts up (no start), pull one spark plug wire, stick an extra spark plug in the wire and lay on the block so it's solidly touching metal. Crank the engine over and see if you've got spark.
Let us know what happens, also it would help if you posted your HP, number of cyl's, and serial #.
HTH.........ed
