My mower runs good till I have to mow the hill witch makes it lean to one side and then it stop and I have to run it with chock on till I get off the hill.. when its level it runs great... can some one please help me ?

Hi,
Afraid on the little info provided, I am shooting a bit in the dark. My guess is that the float is not set correctly or something is restricting fuel flow into the carb.
The effect of choking it draws more gas by increasing the vacuum exerted on the contents of the float bowl.
Peace,
Clarke