help me start my chainsaw?

I have a partner chainsaw mod.351 which is allmost impossible to start, once running its ok but if it stops for any reason its back to normal,this problem is with the engine cold or hot. could anybody please tell me how to tune it, I have phoned the local lawn mower repair experts and they refused to look at it and said "they are a load of crap" please/please/please/ can anyone help me to prove this man wrong