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MX, SX & Off-Road Discussions
Dirt Bike Mods & Maintenance
Clank/knock on deceleration
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[QUOTE="Italian Husky, post: 1479451, member: 146434"] Hi there - I have an air cooled KDX hydrid, the motor is in a converted '89 KX125 chassis. There are many variables on this bike so I'm finding this persistent problem hard to diagnose. The motor is fresh - new nikasil, piston, mains and seals. But it's always made a metallic clanking noise (like a quack sound) when shutting off from full throttle under load. Riding sand trails where I live it's very noticeable. The sound only happens in gear, when the drive/momentum is pushing the piston. It'll rev out without knocking, and won't make the sound if if I pull in the clutch on deceleration. I'm guessing it's firing unburnt gas in the header/main pipe. I don't know why. Some areas of suspicion: - FMF main pipe (as specced for the engine). It doesn't seat all the way in at the cylinder, possibly both o-rings not sealing and allowing blow by under load. - Incorrect ignition timing (timing set wrong, failing CDI, bad plug cap) - Compression too high, or wrong squish for the carb. The head looks standard, But I think the deck has been ground at some point. Compression is what I'll test next. - Fuel - Has a Lectron which seems nicely dialled in all the way through to peak revs. It doesn't idle though, with idle screw fully in. - Non standard air box for the engine (from '89 KX125). Thanks for any thoughts, diagnosing is driving me crazy. Been a long term issue since the build. [/QUOTE]
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MX, SX & Off-Road Discussions
Dirt Bike Mods & Maintenance
Clank/knock on deceleration
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