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Discussion Starter · #1 · (Edited)
Good evening! I am the owner of a 1974 CB200 with just under 1k miles on the odo. The bike runs and rides great after an extensive carburetor overhaul, however it seems something in the charging system is amiss, as it isn't keeping the battery up.

Let's go down a list of everything I've done:
  • I've replaced the fuse by the starter solenoid with one of the spares that came with the bike, even though the old one was OK.
  • I've tested the stator at the yellow and white wire between the pink wire, and both wires start at 12-15VAC and only go up from there with revs.
  • I replaced the rectifier and regulator with a Sparck Moto single-phase 12v regulator/rectifier, even though the original rectifier tested good, I wasn't sure about the regulator.
  • I tested the harness for continuity at every point to make sure that there are no breaks in the harness, including the headlight switch and connector for the alternator. Everything passes.
  • I've tested the battery and it's connections to ensure it's good, and it passes!

Currently, with having my multimeter across the battery, it shows 12.2 volts (battery might be a hair discharged...) and climbs to only 12.3 with revs up to 4k. AFAIK, shouldn't it go up to at least 14v? I come from an automotive background so I'm not used to all these different components. The bike did sit for a long time, hence the low mileage.

I'm afraid to ride it in fear of draining this battery and killing it, I've heard these little batteries are pretty frail. Hoping I can get some help with this, I've been scratching my head over it for months!
 

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Sensei
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12.2 is a discharged battery.....
Charge it fully at 10% of its amperage rating for at least 8 hours (preferably 10 hours) before testing again.....
Since your 200 has (IIRC) a 9 Ah battery , MAXIMUM charging rate is .9 Amps.....
Should read ~13.2+ right when it comes off the charger......
Also should read about 12.6 or 12.7 after "resting" for a couple hours......
IF NOT, replace it.......
 

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Discussion Starter · #3 ·
It read 12.6 in the past, but having started it quite a few many times and not bothered with charging it in a week or so it's obviously discharged, and the starter still turns over the motor just fine. However isn't 12v enough for the regulator to kick on? And regardless if it's discharged or not, shouldn't it show 14v with the bike running at 3k? This battery is brand new, It's only been in the bike for 2 weeks now.
 

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Sensei
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NO...It MIGHT only show about mid to high 12's until over 5K....
Matt should be able to tell you at which voltage the regulator triggers the shunt, but I believe it's 13.2 to mid 13's range...
To get accurate maximum output readings, the battery must be FULLY charged.....
With a low battery, the BIKE is using all or most of the output just to keep running, so no "overage" to charge it back up probably to about 2500/3000 RPM.....
At whatever RPM you show ~25 VAC alternator output is the "break even" rev range...You have to rev higher than that to be charging the battery....
Remember, there is not only a voltage requirement but also an amperage requirement for each running component

Brand new does NOT mean good....about 15% of the batteries I get are bad from the factory + sitting around in the warehouse.....
 

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Discussion Starter · #5 ·
Thank you so much for the information!! I'll let the battery charge overnight and see what the voltage is in the morning.. I had no idea the bike itself used so much just to keep itself running!
Earlier I ran the bike with the headlight on (non-automatic switch) and the light got noticeably brighter with RPM, so the alternator is charging.. Surely a short highway trip would do it no harm!
Thank you again!
 

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There is only basic correlation to car charging systems when dealing with our twins... simple design from long ago that is basically marginal even when all components are working as intended. Think about the advancements in car charging systems in the last 50 years, that helps put it in better context
 
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