It could run rich if you don't have the increased airflow. The basics consist of high flow exhaust and air filter. When you jet all your doing is increasing the amount of gas to the engine which will make it run rich, with more air it will compensate for the gas and should solve your problem assuming the kit was installed correctly. Or maybe you could play with the air/fuel mixture screw and correct it. but the pipe and filter would bring out its full potential that is if you don't already have these.