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Yamaha MX & Off-Road Dirt Bikes
'99 YZ250 suddenly stopped running
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[QUOTE="MXTex, post: 133079, member: 17501"] Yesterday my friends 99 YZ250 suddenly stopped running. I'm looking for tips regarding a troubleshooting process. Here's what I know. - The bike ran well during the first ride of the day. It sounded good quite frankly. - On the sencond ride of the day, I noticed the bike breaking up, (mis-firing) when first entering the track and attempting acceleration. It then cleared it's throat and sounded ok. - About 1/2 lap latter, the motor just stopped. No irregular sounds leading up to this; just stopped and wouldn't start. - When attempting to re-start, the kick starter was very easy to push. I could easily move it through the stroke with my hand. - The bike was bought from a local racer about 6 months ago. The previous owner allegedly had the entire bottom end gone through just prior to sale. Additionally, the top end supposedly had only two rides on it. Vertex piston. - In tearing the bike down to prepare for cylinder removal; I've found the following so far. - When removing the pipe, there was no copper washer betwwen the head pipe and cylinder. Maybe Yamahas don't have these. My Hondas and Kawis do. - Viewing exhaust side of piston shows significant blow by but rings are still in place. - Reed valves look fine. - Spark plug is heavily fouled; black. - Moving motor through stroke via kick starter was easier with spark plug removed indicating that some compression was being generated; but not much. Any help you guys could provide regaring my troubleshooting process and repair would be greatly appreciated. Jim [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
'99 YZ250 suddenly stopped running
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