Author Topic: Knocking Noise  (Read 522 times)

Offline cliff7

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Knocking Noise
« on: June 20, 2020, 04:25:34 PM »
I have recently bought a CB400F2 that is off the road at the moment. It is making a knocking noise at idle (carbs have been stripped and cleaned by a professional and fine balanced by me as best I can). Noise becomes less when put in gear and rear brake lightly applied. After reading various posts about this and not being familiar with this engine I would really appreciate if anybody in the Wirral area would have a listen for me. Petrol/beer tokens gladly supplied. I think it might be primary chain but not sure. I don't want to strip the engine yet if it will be ok for a while.

Offline Johnwebley

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Re: Knocking Noise
« Reply #1 on: June 20, 2020, 04:32:10 PM »
Likely just normal clutch rattles.

All of the fours suffer .

Need to sync carbs with gauges.
Also check timing and tappets

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Offline Bryanj

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Re: Knocking Noise
« Reply #2 on: June 20, 2020, 05:39:57 PM »
John you got that the wrong way round, carb sync is at the bottom of the full service list

Offline Johnwebley

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Re: Knocking Noise
« Reply #3 on: June 20, 2020, 06:03:36 PM »
I am an amateur compared to you.

I can't be perfect


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Offline Bryanj

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Re: Knocking Noise
« Reply #4 on: June 20, 2020, 06:39:17 PM »
Why not others are!!

When in trade i refused to do just a carb balance no matter how much the owner insistead the tappets, timing, points gap and cam chain were all "perfectly correct"  They rarely were by the way

Offline cliff7

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Re: Knocking Noise
« Reply #5 on: June 20, 2020, 07:17:39 PM »
I'm only a (ex) car mechanic and it was always mechanical (compression, valve timing and clearances), then electrical (points, timing) then carb(s) last. Last time I set timing on a bike it was using a marked stick down the plughole. A bit different with this modern (1978) stuff!

Offline cliff7

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Re: Knocking Noise
« Reply #6 on: June 20, 2020, 07:19:35 PM »
Noise doesn't get louder after removing dipstick.

 

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