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Message: [QUOTE="genus727, post: 1259833, member: 83681"] This 1981 Yamaha YZ 465 is my first 2-stroke and I just finished a top-end rebuild (piston was seized by previous owner). I got all excited and took it out to the beach (Oceano, CA) to mob around and test it out. It started out great, but after 15 minutes of good riding (at higher-throttle) the engine just dies. I'm at first concerned that I hot-seized it, but I can still kick the bike through it's stroke. The only thing is that it's now about 5x easier to kick the bike, like there is very little compression. When I try and kick-start it I get no life from the engine. Only the occasional backfire, which indicates to me that the electrics are still good. I inspected the plug and it looks good. Any idea about what I did to this bike? What would cause the compression to go like this? I don't see how I could have burned through or cracked a piston in 15 minutes of hot-riding. [/QUOTE]