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sturgill_252

2008 yz450f loss of compression

4 posts in this topic

Bike jus had a new top end rebuild along with cam chain and bike ran great for 2 rides and i started it with my hand it has less power and bogs some. i havent cranked it since the day at the track. my opinion i think it is something to do with the auto decompressioner. it doesnt close quickly. when i wire it open the bike has so much compression i cant kick it over.and it also jus had intake valves.

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Could be a cam timing problem.  The AD mechanism doesn't "close" at all while cranking, and is fully active until 700 RPM, at which point it disengages.  There is virtually nothing that ever goes wrong with the device.  However, the system is dependent on cam timing, and if the exhaust cam becomes one tooth retarded (not rotated forward far enough), the bike will have nearly no compression at cranking speeds.  That would also account for the lack of power.

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Could be a cam timing problem.  The AD mechanism doesn't "close" at all while cranking, and is fully active until 700 RPM, at which point it disengages.  There is virtually nothing that ever goes wrong with the device.  However, the system is dependent on cam timing, and if the exhaust cam becomes one tooth retarded (not rotated forward far enough), the bike will have nearly no compression at cranking speeds.  That would also account for the lack of power.

Thanks i pulled the head and discovered it was a broke valve spring. If you could read my other post about my practice bike and help if possible i would appreciate it sir.

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If you want me to look at something, post a link.  I'm not inclined to search for it.

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