Engine rattle when idle

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Max
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Engine rattle when idle

Post by Max »

Hi

I'm pretty new to the forum. I just finish to restore a CBX '79.
It started on first try and it idle normally. However, when idle it makes a sporadic rattle, both with clutch engaged or not.
It seems a chain noise but all the internal chains are brand new and I did adjust both the chain tensioner (front and rear).
I did the usual test (timing, cylinder pressure, etc) and the carbs were completely rebuild.
You can hear in the video the rattle.
Does anybody has an idea what can be the problem?
Thanks


https://youtu.be/OT313LWlr2c

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NobleHops
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Re: Engine rattle when idle

Post by NobleHops »

There's a lot going on in the bottom end of these '79 engines that makes them rattle, certainly the worn-out clutch dampers, but also the primary chain, and the primary shaft itself. A careful synchronization of the carburetors plus replacement of the rubber clutch dampers can both improve things, but to a certain extent on an old '79 it's a case of "they all do that" to some degree. Do the damper project and the sync if it's bugging you and then "enjoy your motorcycle" is the best advice I can offer you.

N.
Nils Menten
Tucson, Arizona, USA '80 CBX, sort-of restored :-)

steve murdoch icoa #5322
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Re: Engine rattle when idle

Post by steve murdoch icoa #5322 »

Hi Max.
Agree with Nils it might be clutch rubbers.
You can get them from Bert at SixCenter.
https://www.sixcenter.nl/index.html

Sounds like there also might be a bit of an exhaust leak.

Max
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Re: Engine rattle when idle

Post by Max »

Thank you to both of you.
I will certainly buy the rubber dampener and sync the carbs.
I discovered that cylinder 2 and 6 don't work, which probably doesn't help the quietness. Spark is good.
Carbs have been entirely rebuild and jets changed.
Modified the air screw but they are still dead.

Any suggestion?
Thanks

steve murdoch icoa #5322
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Re: Engine rattle when idle

Post by steve murdoch icoa #5322 »

Does "new jets" mean different size?
How did you modify the "air screw"?

Are you using the stock airbox and filter?

daves79x
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Re: Engine rattle when idle

Post by daves79x »

I'd say you still have carb problems. Low-speed circuits still plugged. 'Changed jets' and 'modified air screws' scares me too. You can read volumes here about everything you've asked about.

Dave

Max
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Re: Engine rattle when idle

Post by Max »

I didn't modified anything. Air box is standard as well as everything else.
I meant that i adjusted the air screw to see if there were changes.

However, I found the problem. During the rebuild I wrongly inverted 2 spark wires. Now it runs very well and smoothly.
No more noise and rattle as well.
Thanks for the help.

steve murdoch icoa #5322
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Re: Engine rattle when idle

Post by steve murdoch icoa #5322 »

Glad you got it sorted.
When you get it finished post a pic or three.

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