How can I fix my snow blower engine ?????? ?

I have trouble with my Tecuseh 10.5 horse pover snow blover engine. It is equipped with a carburator that has no hi speed or low speed adjustment screws .When it runs it keeps hunting, the engine will not run steady and will not idle properly. It has lots of power but the throttle has to be almost wide open to keep it running . Does anybody know how to correct the broblem?