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Light Engine Knocking

Derk

Derk

CB750 Member
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Blainville
Hi all, my 74, runs and starts great. But I have an issue , when I decelerate at slow speed, I can hear a sort of light engine knocking, that immediately stops when accelerate again. It only happens when decelerating.
Can anyone help me
Merci.
 
Might be hard to find if it only happens while decelerating. Check/ listen for things like exhaust leaks. Is it a constant sound that happens multiple times per deceleration or is it a one and gone thing?
 
Its going to be really hard to diagnose without hearing it. Anything from bearings to wrist pins to cam bearing clearance to the transmission or clutch or loose cam chain or loose primary chains can all make noise when decelerating. Maybe check valve clearances and timing chain tension first just to rule out the simple stuff. Pull the plugs and see if they are clean or carboned up as excess carbon in the combustion chamber can cause light knocking as well especially if the bearing clearances are getting on the loose side.
 
brettp said:
Might be hard to find if it only happens while decelerating. Check/ listen for things like exhaust leaks. Is it a constant sound that happens multiple times per deceleration or is it a one and gone thing?
Click to expand...
Thanks Brett, indeed only when decelarating, exhaust have been restored and are fine. it is a one and going thing in french the word is cliquetis...if that can help. as it is light.
 
dirtdigger said:
Its going to be really hard to diagnose without hearing it. Anything from bearings to wrist pins to cam bearing clearance to the transmission or clutch or loose cam chain or loose primary chains can all make noise when decelerating. Maybe check valve clearances and timing chain tension first just to rule out the simple stuff. Pull the plugs and see if they are clean or carboned up as excess carbon in the combustion chamber can cause light knocking as well especially if the bearing clearances are getting on the loose side.
Click to expand...
Hi Dirtdigger, Thanks for your full reply, a lot of your suggestions are out of my skills I will have to check them with my mechanic. Plugs are new.
 
Can you reproduce the sound of you rev the bike in neutral and let go of the throttle?
 
Brett hit on the first thing I thought of. Check your sprockets and chain for condition etc.
 

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To me, that sprocket looks OK. How much does the middle of the chain (on the bottom half) rise when pushed up?
 

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