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MX | Off-Road Gear Info & Reviews
engine mods by pro-circuit
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[QUOTE="MX145, post: 295499, member: 27247"] I sent my '02 YZ125 head & cylinder into Pro Circuit for some mod's. I requested for more mid to top end performance since that is where I ride the bike at. I was impressed, as well as my brother, which also owns a '02 YZ125. There was a significant gain as well as response. My bike now seems to also have more bottom end than his even though that wasn't what I was specifically looking for. Be prepared once you get it back to be able to gap the rings to the specified clearance (not hard, but requires a few tools). You will also have to get new needles, jets, and run race gas. Recently I've been running my bike at our local test track and indoor arena-cross and the performance has been top notch. I haven't been able to run it on an outdoor MX track yet, but I'm positive it will perform even better there. Last fall, at one of the outdoor tracks they have an uphill double that once I lowered my rear sprocket teeth it made a huge difference. I was able to then hit it in 5th wide open instead of 4th/5th with some bog. If you haven't already changed the gearing, I would go for that with a new required chain and see if that helps any. I raced last fall on a stock '02 YZ125 with only a change in handlebars and rear sprocket/chain and did pretty well considering there wasn't any aftermarket acc. or performance products for the all new redesigned bike. I even had to make my own black backgrounds since those weren't available at the time. Now you can get almost anything for them. These bikes RIP !! and you can make them haul BOOTY!! I don't know of any programs for you to use in order to port the '02 YZ125 motor for your specifications. I leave it up to the guys that do it everyday. If you leave your engine stock, I would recommend a new reed cage/rad valve rather than a pipe & silencer. You will get better performance off it for your money than an aftermarket pipe & silencer. If you go for the mod's then you might want the pipe & silencer and maybe even go with the reed cage/rad valve as well. It really all depends on what you are looking for. The stock pipes are really good nowdays it seems. I was happy with the overall performance before all the mod's I have done and now LUV it. I can't wait to ride. [/QUOTE]
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MX | Off-Road Gear Info & Reviews
engine mods by pro-circuit
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