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Hiya.

KDX220. Just had cylinder replated and new piston. Got an erratic knock sound coming from exhaust ONLY on deceleration from anything but low revs. Knock, knock... knock... knock... knock, knock, knock... etc. Plenty of random gaps in between the knock sound.

Clutch in and sound goes away. Hit kill switch and sound stops. That makes me think non-mechanical and gas flow/load related.

Have leak tested engine, checked exhaust header to manifold / tried a clip richer on needle along with much air screw faffing - no bad problem / no change.

If it did this before the re-plate and new piston, it sure wasn't as obvious... Ideas?

(At a guess - porting affected by replate? Also, 'Exhaust Bang' on 2Ts seems to be a common occurrence - some say not to worry about it. Looks like some fix by going richer/leaner or by changing cylinder base gasket to alter squish.)

Cheers.

I just did a replate/piston on my 220 and notice a slight clink/knock on deceleration. In my case I think it's the kips sticking and then releasing. I noticed during assembly it didn't function quite as smooth as before because of the rough texture of the passages ( bead blasted) after the replate. Don't have much time on it - temp 5 below here today!-but am hoping it'll self polish and free up with a little use. Everything else's is stock on this bike.

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Description does sound like kips rattle.

And kips rattle would stop when I clutch in or hit the kill switch?

Also, this isn't a rattle sound (fast and constant) - it's a random, erratic knock sound with fair size gaps in between 1 or 2, 3 knocks together. Cheers.

You just redid the top end, have you checked compression after? New plug or the old one? You checked your crank side clearance, ring end gap, new wrist bearing and clips? Maybe try and get some video/audio and post it up. Engine noises can be tricky to diagnose by description only.

I'll try get some audio... Pretty sure it's fuel igniting in header. I'll try a new plug - though this one isn't old. Rest is OK.

Tried a new spark but same. I can hear it real clear when riding but it's muffled in with general engine noise when I record so doesn't sound like much.

crs wrote:And kips rattle would stop when I clutch in or hit the kill switch?

Yes, kip rattle stops when you pull in the clutch. I don't think anyone has ever really figured out why. Also, running a full quart in the trans seems to help.