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Discussion Starter #1
Just fired up my 78 cb400A for the first time since I bought it and have been rebuilding it. I haven't done any work to the engine, only mostly cosmetic and mechanical stuff like cables and brakes etc... Also rebuilt the carb.

It runs fine but still needs to be tuned. I did however notice this disturbing clunking noise on the top end at lower throttle speeds. I'm afraid I'm going to have to rebuild the top end just by the sound. But can anyone help me by trying to pin point it? Sounds more like rocker or valve noise than piston noise, seems to be right under the rocker cover.

Can't seem to upload the video from my phone here so I've attached a YouTube link of it. (Which hopefully works)
Thanks
Eric


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You might try adjusting the timing chain and or the valves . The As not that hard to work on and you can rebuild the top end without removing the motor.

You will need a FSM. If you remove the valve cover I find it helps to move the coils out of the way. Just a thought.

Bill
 

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Valves and chain need adjusting anyway. The sound appears to be absent at idle, only there when throttle is opened slightly. Sound might be an exhaust leak, check the header gaskets.
 

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Are you sure it's in the top end ? right at the end when the motor shuts down you can hear what sounds like the starter coming to a halt.
 

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That sure sounds like an exhaust popping to me. I think you need to revisit your carb rebuild.
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Discussion Starter #6
It is difficult to tell in the video, but it is absolutely coming from inside the valve cover.
 
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