I took a petrol lawnmower off of a friend who said that there was something wrong with it, got it home and found that the head gasket had gone, so I got a new one and put it on and changed the spark plug, put it back together and tried to start it and nothing, took the air filter off and tried again and it started and it runs, a bit lumpy, but it runs just sounds like its drowning itself in petrol. So I took the carb off and changed the diaphragm, put it back together and still the same problem. So I changed the gasket on the inlet manifold. But still the same problem, if I start the mower with the air filter off and as soon as the air filter gets anywhere near the carb the mower dies, the air filter 9 times out of 10 doesn't even get to be placed on the carb. I checked the spark plug and it was black, so I gave it a clean. It has no choke or any adjustment screws. Has any got any ideas, as I'm running out. They will be greatly received.