I have a Poulan Pro with a 17.5 hp Brigss Straton runs good until mower is put under a loud ( blades, Drive and under mowing condition) cuts out, spits and sputters. Complete cleaning of Carb helps, recharged battery and can only get to run by feathering the chocke. Any ideas, this is not related to any safety switches and is strange that chocking down the motor keeps it running.