Some of the problems I've heard about (and some I've experienced)-- fuel level float coming off and damaging the fuel pump; AIS backfiring (not causing damage, but annoying); the dreaded bog on '14+ machines; and the overall weight of the machine. For the fuel level float, you can remove the pump and remove the float before it breaks, and you'll be fine, but you won't have a functioning "low fuel level" light anymore. I wouldn't worry about it, but some people like having it. For the AIS, most people will delete it, which is really easy. You can either block it off with a homemade block off plate or with a different block off. You can also use the 2009-2013 cable hanger there in place of the '14+ piece. For the bog, the only fix I've seen firsthand is the Vortex controller. I know that Vortex fans (like me) will possibly upset some people with their comments or constant praise for it, but it really does work. I've never had better throttle response. As for the weight of the machine, there isn't really a whole lot you can do that doesn't cost an arm and a leg. Titanium parts weigh less than their steel counterparts, but will cost you a ton... and if you're not racing on a professional level, then it's hard to justify that kind of investment. Even if you ARE racing professionally, it may not be worth your time or money to replace steel fasteners with titanium ones. One problem that I encountered, is the high seat height. I've heard of people lowering the subframes on other machines, but it would be really difficult to do on the YFZR if you wanted to keep the stock subframe. Instead of lowering the subframe, I extended my shock linkage. It lowered the rear a bit and I like the riding position quite a bit more now. I still plan on raising the bars, by way of a taller steering stem (modified stock stem), and mounting my Precision stabilizer, but not in the prescribed mounting position, as I think it looks silly hanging off the side, over the left upper a arm. Another problem I've experienced is the breather issue, which is common. I have an LT-R breather, but I haven't mounted it yet. I currently have a UNI breather up by my steering stem mount, but it pukes a little oil every now and then if I ride it hard for very long. Once the LT-R breather is installed, I believe this won't be an issue for me. The plastics may be an issue for some people, as the earlier plastics left the frame uncovered where your knees hit if you're cornering hard, and I've gone home with black and blue marks because of it. The '14+ plastics remedy this issue, and a couple others, by pushing the front fenders further forward, and the rear fenders are a little smoother to transition from the seat to the fender during aggressive cornering. The machine, in my opinion is very good, and is obviously very capable, as demonstrated by Chad Wienen for the third year in a row. I'd still like to break everything down and see exactly where all the extra weight sits, as my carbed '06 seemed to be much lighter, but I went through EXTENSIVE lightening measures. I'm not prepared to go that in-depth on my new machine. I'd like to compare overall weight and the weight of each component between the carbed machine and the FI unit. Maybe then it would be easy to determine a solution. A lithium-iron-phosphate battery will be considerably lighter than the stock unit, so there's that. Anyway, I hope this helps. Have fun, everyone.