Jet Kits rock. Okay, here's why I like them. My 10yo CBR600 was a good bike, it did what I wanted. However it was lethargic below 6500rpm, with a noticible dip between 5500 and 6500 rpm. Above that it went well with enough to keep me entertained. This meant running about town in second was not brisk as what it should be, whilst first was too jerky and direct to enjoy. It was enough for me to dream about other bikes and think about how good the power delivery would be. I tried a K&N air filter in it to remove the power dip from 5500rpm, but it didn't do much apart from help the breathing at higher rpm. Carb cleaning and balancing didn't help that much either. I was rather sure at this stage that the bike wasn't fueling correctly. I booked the CBR in for a Factory jet kit to be fitted at Raceway Suzuki by Tony - he used to race the a CBR. Tony also cleaned the air filter, did an oil and filter change, inspected the plugs whilst fitting the jet kit. The kit, fitting and general service cost $550ish (bargain considering the kit is worth $250). Wow, what a different bike it was. Not only was the engine looked after but lots of extra little details were attended to. Riding home I opened the bike up in second gear, normally this would result in strong acceleration. This time the acceleration was noticibly stronger, strong enough to have the front wheel skimming off the deck at about a ton with three grand before redline. There was still more throttle available if I'd wanted it. Around town the CBR will now run smoothly in second from about 2500rpm, without any snatchyness - a small amount was previously noticable. From 2500rpm to 6500rpm is now useable which make low speed riding much more pleasent. Above 6500rpm the bike generally has more go, part throttle pick up is much, much more crisp. The jet kit and fitting is possibly the best $550 I've spent on the bike and I'd highly recommend getting one fitted on any carbied bike with breathing mods.