I just purchased a slip on from TC RACING. There good at building four-strokes and they do Doug Gust's motor work on his Z400. If you purchased this, How do you like it? They said to cut a hole about the size of a silver dollar on the lid near the snorkel and put a 140 main jet and might need a 155. Thats with the snorkel on too and with a K&N air filter. Well I'll let ya'll know how it is and talk to you later. The slip-on are about $340. Talk to ya'll later.