Flymo L400 dies, have to pump primer to keep it going!?

My mower wouldn't start this year and I guessed it would be congealed oil some where. I took the carb off and soaked it in neat petrol and blew out any muck I could see, took off one cover and cleaned but left the diaphragm as it was stuck on solid and didn't want to damage the seal. Put it back together and it started only to die soon after. If I start it and keep gently pumping the primer it will run, as soon as I stop it stops. If I pump the primer when the engine is hot but not running running it sounds as if the fuel is going straight into the engine and hitting something hot as it sizzles. Have I missed some blockage or have I put the spacer between engine and carb on the wrong way round, or some other silly mistake?
Does anyone have an exploded diagram of the carb?