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Discussion Starter #1
I'm near the end of a long rebuild of my cb360 1974. Its going well and the bike generally runs well. The only problem I have now is a strange, intermittent power failure whilst at speed. If I take the bike out it runs fine for the first 10 minutes or so, then the engine starts to falter, power cutting out and coming back, worsening until it just dies and I glide to a stop. The instrument lights have become dim and the engine is dull when I try to kick start. Sometimes if i turn off the ignition for 5 minutes and then turn it on again power is back up, lights are bright and I can get going again, only to find the problem return 3 miles down the road.. The battery seems to be holding its charge as the power always seems to come back, even if its an hour later in the workshop. Maybe its a loose connection or something but I've got no idea where to start looking. Could anyone please suggest some likely causes? Thanks, Hawksmoor
 

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Since the battery bounces back, it seems that the charging system is not working at full capacity or possibly not at all. Have you changed the separate rectifier and regulator pieces to a modern rec/reg combo? That's a good place to start if not
 

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Try opening the fuel filler cap. Vent may be plugged causing vacuum to build up in the tank. Sitting for a few minutes allows enough air in to allow you to go another few minutes.
 

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Do any of the lights misbehave when the handle bars are turned lock to lock, maybe the neutral light flashes on and off ??

When engine is running from cold, does the headlight grow bright when the engine is revved from idle to say 4 k revs, and, the voltage across the battery increases when revved??

You have painted the frame etc.?
 

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Discussion Starter #6
Hi, thanks for your responses. Drydreamer, non of those things happen with the lights but I have painted the frame. I did remove paint away at earth connections but I guess it still could be an earthing problem.. AD.. I havent changed the original rectifier and regulator but I am planning to this weekend, I ordered a new part from sparck moto. I hope this solves the problem. C.. youre not the first to suggest a loose neg batt terminal, i'll examine this again. J-T, ill try the fuel cap but I think its an electrical thing rather than fuel. I'll let you know, thanks again, H
 

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From the symptoms I would surmise it could be due to a melted wire that increases resistance to current as it becomes hot. Check for discolored wires or connectors between battery and headlamp. Those wires that move when the handlebars turn might have some broken strands inside the sheathing. Does the same symptom occur when the bike is stationary and idling?

Another possibility is some corrosion in the fuse panel. I agree the fuel vent atop the tank could cause the engine to falter due to fuel starvation, while the electrical failure could be a secondary fault.
 

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Have you checked that the battery is recharging when you twist the throttle?

I would bring a multimeter on your next ride and check the battery after the bike dies to help confirm if this is an electrical issue vs fuel delivery.

I've had similar issues: once due to loose connections at the battery terminals and once due to fuel starvation from poorly routed fuel hose and a gummed up gas cap that caused a vacuum issue. For the latter, fuel was flowing, just not fast enough to keep up at cruising speed. It would eventually die but then restart after a few minutes once the bowls slowly filled up.
 
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