Hi, I've a Suzuki Z400 QuadSport with a Pulse Charger full exhaust, no airbox lid and no snorkel, Pro Design Pro-Flow foam filter, and a FCR39-MX pre-tuned by Sparks Racing. I'm using a 165 main jet, needle on 3rd clip and 55 pilot (the factory settings). It's a bit rich, and I think it'd be necessary to drop to a 155 main jet. My question is, how much does a rich mixture affects to performance? A friend of mine, who is a mechanic, has told me that a slighty-rich mixture (as mine) can drop around 2 hp in the Z400. I think it's too much, and the difference between a perfect-jetted and a slighty-rich (for example a main 5% bigger than the perfect one) engine could be 0.5 hp at the most. What do you think? A before-after dyno graph would be very a perfect explanation.