McCullach TrimMac 210 Carb?

Hi, A friend asked me to look at his strimmer which will not run. It starts eventually and will run for a few seconds then die. I have flushed the tank, changed the fuel, cleaned and checked the spark plug (looks damp after a while but think that just me having the choke on to start it!?). It is choosey as to when it will start-sometime full choke others no choke, tried with or without the air filter and still the same. I even started to strip the damn thing down and noticed that there is a slight tear in the membrane/Gasket behind the air filter. The only other thing i am thinking is that i may need to overhaul the Carb if this is possible? Or is this a job that i should have never taken on. Any advice would be appreciated