Starting problem when warm

[Budeboy]

I have a McCoullach 18 inch with BandS 450series 8 years old. Has always started easily cold or warm. Recently started to hunt running too rich. Changed diaphragm and gasket, now starts 1or 2 pulls from cold runs perfectly until stopped to empty box. Afterwards when warm will not start at all. Tried no choke half and full choke and primed. Leave for app 15 mins starts and runs perfectly. Any suggestions much appreciated

 

[ILENGINE]

I would probably remove the spark plug when warm and have somebody crank the mower to see if you have spark. Could also try putting a small amount of gas into the intake and see if it starts. If it starts with the fuel then most likely a carb issue, but I am leaning toward a heat sink issue with the ignition and loosing spark.