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Slapping sound from the top end...

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Hey all, I have a GB500 (for which I could not find an active forum and I know the XR has a similar motor) so I wanted to ask you all about this intermittent slapping sound coming from the top end when it is warmed up, video is here:

https://youtu.be/NHdEI5sZats

Any idea what it could be before I crack open the motor?

Thanks in advance!

Edited by MOTOBLN

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Lot going on there.

Turn the idle down and adjust the valves (when cold)

is that smoke from the exhaust or engine?

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Cam chain is loose and it sounds like some excess valve lash. 

Maybe a bad sprag in the cam tensioner assembly causing that cam chain slap.  The cam chain could also just be worn out.

Not many of those bikes around the US I'd bet.  Cool to see someone with one.

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Cam chain tensioner one way bearing is slipping and releasing tension on the chain. Replace the tensioner arm and pivot shaft.  

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What are the two covers for under each exhaust pipe mount, at head, they have two bolts on each cover.

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2 hours ago, bork said:

What are the two covers for under each exhaust pipe mount, at head, they have two bolts on each cover.

I believe they are for blocking off the emissions system for us California bikes 🙄

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19 hours ago, bork said:

What are the two covers for under each exhaust pipe mount, at head, they have two bolts on each cover.

Air injection into the exhaust ports.  There's no gain in removing it , other than weight loss , but it does make some bikes pop when you suddenly close the throttle. Everybody blocks the ports off to get rid of the excess crap that goes along with it. It's not only California and cars have had it for decades.

Edited by JoeRC51

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I adjusted the valves and poked around the cylinder head and didn't notice anything glaringly obvious except for some pitting on the rocker arm lobes. When I put it back together, the original trouble seemed to go away, but now during idle the bike clicks and just shuts off:

Any ideas?

Thanks

 

Edited by MOTOBLN

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Decompression look ok when you where in there?

Sounds like it might be involved.

It sounds just like mine...... it stalls from a dead cold start when I give it gas too soon................stall.....click .......................just like yours

Edited by EarthCruzn

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It may be activating because it's idling too low. It's seems to do it as it's about to stall.

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