Sputtering or choking on acceleration after new muffler GY6 150cc

150cc GY6. I bought a new muffler off amazon. It is a little bigger than the last one but that doesn't matter right? Well, it is having trouble when I go to accelerate. It is like coughing. if I increase slowly it seems to be fine. Do I need bigger jets in the carb? or what do you think it is?