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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Yamaha Powervavle Pictures
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[QUOTE="kx125412, post: 1194145, member: 68341"] Little pits sounds like your main or rod bearings are toast. It happened to me on my ol RM125 before she gave up. I got one last drag race out of it and then it blew, I smoked this kid on his 250 mind you the 250 was a 78. Anyways, the powervalve should only rotate a quarter of a turn. That's all these YZ's need to open the valve fully. For the valve to open to far it has to do almost a 360 degree turn to come back into the exhaust port but when it closes it can come into contact with the piston quick if its coming to far in. Unhook the governer and just turn the valve by hand it should only move a quarter of a turn. I'll get pictures up later today on what the tabs look like. Its much easier to see how the exhaust valve works with the jug off. [/QUOTE]
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Forums
Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Yamaha Powervavle Pictures
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