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Discussion Starter · #1 ·
Hi all, first post here but ive been lurking for a bit--- this forum has been really helpful so far. I recently bought a great 73 cb350 but have been chasing down electrical problems that have kept me off the road the past few weeks.

Very suddenly my bike has been blowing its fuse. Originally it happened whenever i turned the key on, but now i can start it up fine but it blows when i rev the engine. As im waiting for a new rectifier regulator unit, the charging system is unplugged as doesnt contribute at all to system voltage. I cant find any apparent shorts either. Does anyone know what this could be?
 

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Discussion Starter · #2 ·
I should note that this began immediately after an incident where my battery overheated at the positive terminal and melted through the rubber sheet i use to insulate the terminals. When the battery is plugged in and key is off, the positive terminal has continuity to ground, but when the battery is removed, the positive terminal connection on the bike has no continuity to ground. Could the battery be the issue? Could it be shorting itself? It is a sealed agm type battery. Before disconnecting my charging system as mentioned above, i discovered that my regulator/rectifier was bad. Could i have toasted the battery at some point and now it could be blowing my fuse out when under load?
 

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I would not try starting again until you replaced the regulator and rectifier. The regulator is most likely the cause of your fuses blowing when revving since its job is to regulate the amount of voltage produced by the alternator/stator. Too much voltage and you start frying stuff and the fuses are suppose to safeguard against that.
 

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Discussion Starter · #4 ·
True. But as i mentioned in my first post, the stator is disconnected from the whole system as is the rectifier regulator. So no contribution from the charging system.
 

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Hey alehman. I'm attaching a copy of a wiring diagram for your CB. What I'm look at is if you have taken out the stator, reg/rec from the system then it is all being run off the AGM battery. All of your spark and power is coming off the battery. That's a lot of load and its possible that you are overheating the battery and popping the fuse with that amount of draw. What size fuse is it blowing? What is the charge state of the battery when it blows the fuse? In any case if it were my whip I would certainly not run it until I get the reg/rec back in order and sort the wiring.

Floor plan Plan Line Technical drawing Parallel
 

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Discussion Starter · #6 ·
Hi ScramblerCurtis, I purchased what I thought were 15A fuses but I realized yesterday when I looked at the packaging that the person behind the counter had given me a box of 30A fuses. So the 30A ones have been blowing. I've now switched back to 15A. In answer to your other question, the battery is freshly charged.

Now the bike is back to popping the fuse whenever I turn the key on. I'm going to keep tracing wires throughout the bike... :( Any advice is greatly appreciated!

In your opinion do I risk damaging my new R/R when I plug it in to a system that seems to have a short?
 

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@alehman I think that you have a short somewhere. Check all of your ground points and check your voltage from your battery. Should be 12.6 or so. And I would not install and plug everything in through the new R/R and stator until you have your ground short issue fixed. It almost sounds like you have something wired backwards or connected backwards. try and trace your wires from the battery to the switch and through to the coils.
 

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I would say an intermittent short somewhere. When you rev the engine everything vibrates just enough to cause the short again. Sometimes the wire welds itself to the frame etc. and then when you turn on the key POW.
 

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Discussion Starter · #9 ·
It is definitely intermittent but i do wonder if it is a short. When i remove the battery there is no continuity between the bikes positive lead and ground. I even tried shaking the bike around to get a reading if it is an intermittent short--- but my multimeter doesnt show any continuity whatsoever til i turn the key on. Can a bad battery discharge too much and overload a fuse? I have a new battery in the mail so one way or another ill find out... anyone have experience with that ot know if its sound in theory?
 

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Discussion Starter · #10 · (Edited)
Then again... i guess that means my short could be downstream of my key switch. When i unplug my key switch, all wires but red have continuity to ground with very low resistance. Are all three of those circuits shorted or should they have continuity to ground??
 
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