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Discussion Starter · #1 ·
Hi,

I’m having a reoccurring issue with a CB350, which is cutting out when idling.

It’s been a couple of months since I last rode it, and I took it out today through the city, having to deal with a lot of red lights, etc. It started easily and everything was running smoothly, but after half an hour it started to die when stopping and idling at the lights. It would idle for a minute then instantly die. No splutters or pops. The starter began to slow so I had to use the kick.

It’s happy to ride above 3k and will sit at the lights if you keep blipping the throttle, but let it sit and it’ll eventually decide to call it a day.

I tested the battery when I got home and it was down to 11.8v. I started it up and revved above 3k and I could see the alternator getting up to 14V so I imagine the charging system is okay. The battery is a brand new one another CB I have and is the exact spec for the bike.

Could there be something draining the battery whilst the powers on that is more than the charging system can deal with, and if so how can I fault find it? On my old VW i’d hook a MM up to the battery to check the current flow and pull the fuses one at a time, but not sure about motorcycles!

I can’t imagine the charging system
is so poor it can’t handle a few traffic lights with the main beam on, is it?

Any help would be great thanks!
 

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check water level and charge the battery.

put a meter on the battery and crank it over. Does the battery drop below 10 volts? if so, battery is bad. you can also take the battery to an auto parts store for load testing. meter tells you only voltage, not if the battery has enough amperage.
 

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Discussion Starter · #3 ·
Thanks for the reply!

I forgot to add in my first post that when I started the bike up I had the tester on it and it went from 11.8v down to around 10v but didn’t drop below that.

The battery was a refill type, pour the acid in then charge it up. It’s only been on the bike for a few miles.

I’ve got it on charge now. Tomorrow i’ll hook it back up and test it when cranking.
 

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Discussion Starter · #4 ·
Also.... this problem is one I had with the previous battery too. It was the one that came with the bike but would still hold charge up to 12.6V when put on a charger. I’ve just swapped it over with a new battery to see if the problem still persisted and, unfortunately, it does.
 

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I have a similar issue and from what I've gathered from my limited time here on the site it's a common point of failure in these old bikes most people have upgraded to a Rick's charging system (regulator/rectifier and stator.)
Apparently the stock charging system barely breaks even and it's at least recommended to change your lights to LEDs for less draw on the battery if it's not in your budget to replace the charging system
 

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Discussion Starter · #6 ·
Thanks smikkleson. I’ve read that too and I think you’re right about having to do some upgrades! I guess I found it rather unbelievable that Honda would have designed the stock charging system on a full battery to only allow for 30 mins of city riding with the lights on before it started running out of juice. Was it like this straight out of the factory?

I will test the rectifier to check the diodes are operating properly, and also test the current from the rectifier to the battery whilst the engine is running.

Before that I wonder if it is worth measuring how much current the bike uses by running the bike with the alternator disconnected and measuring the current?

After that I could clean up all the contacts and check all ground connections, etc and see if there’s an improvement?

I think i’d like to eradicate any short or leaky current first or at least establishing if there’s a fault adding to the current draw before changing anything like LED lights, etc.
 

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Do you still have the original Rectifier on the bike.
The diodes in the original deteriorate over time and lose their functionality.
Their purpose is to convert the AC Voltage create by the charging system into the required DC Voltage.

At best when they were NEW they were about 75-80% efficient.
After 40 year they are probably down to 50% efficient at best.
But that was what was available for components back then.

Today there are several choices you can use to replace them.
These tend to be 80 - 90% efficient and you will see a marked difference with them.

Common Motor collective sells a replacement combination Rectifier/Regulator that would be my recommendation.
I have that on both my bike & my sons and they perform very well.
While the charging system still doesn't get much above break even when under 3K RPM that is the nature of the beast.

Also make sure when you are riding that you keep your RPM's up over 3K while in the city.
You may find you rarely get out of 2nd gear but you need to understand these motors are happiest running in the 4K-7K RPM range.
So ... it may boil down to your riding style.
 

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The system design is adequate but as stated, age deteriorates electronics and the connections so it is a lot less efficient. It was not designed to kill a good battery in 30 minutes and it shouldn't. Clean all connections going to the battery. Maybe even check to see if there is a parasitic draw on the battery. Old components can have a corrosion "short", not enough to blow a fuse but enough to have an excessive pull on the battery.
 

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Discussion Starter · #10 ·
Thank you for the replies. It’s good to get some feedback.

Yendor - You have a very valid point about riding style when cruising through town. I do have a habit of rolling under 4K, so I will bear that in mind for the future thanks.

76TWIN - Thanks for the recommendations. The original reg/rec has been replaced by a modern upgrade, which does look like CMC one, but with no history on the bike it is hard to tell exactly.

Jd50i - Parasitic draw is definite concern. The electrics look okay with no major butchering, but having tested the battery with the key in OFF, there was 0.00A at both 10A and 100mA setting.
 

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Discussion Starter · #11 ·
So I have done some testing with a battery charged to 12.9v and this is what I have found.

1 - No current draw with key in OFF position.

2.5A with key in ON position and lights OFF.

5.8A with key in ON and lights ON. This increase of around 3.3A would be in keeping with the addition of a 37W headlight and 7W tailight.

2 - Continuity in stator cools is good.
No continuity between stator coils and ground.

3 - Reg/Rec has consistent continuity across diodes (YELLOW & PINK) between Ground (GREEN) and Power (RED) in one direction only.

4 - The Reg/Rec puts out 14.5V at 3K, with a charging current of around 1A (this is a bit jumpy but stays mainly just over 1A.) This would appear to be standard according to the alternator charging graphs in the Honda Shop Manual.


Not certain what I can deduce from all of this. Stator seems fine. Reg/Rec is working as it should I guess. Battery is able to hold a charge. There’s no current being drawn until the key is in the ignition.

Is 2.5A a lot of current in the ON position? That’s about 30W. The neutral light is on. What else?

Any thoughts would be extremely helpful. I’m not totally sure that I haven’t missed something.
 

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Power - ON with the switch will energize at least one of the coils depending on whether one or both of the points are closed, and the position of your KILL Switch.

That would be your 2.5 AMPS.
 

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Discussion Starter · #13 ·
Thanks Yendor. That makes sense. The kill switch was on as I had been running the engine for tests. I’ll test with the kill on off, but it would seem that everything seems normal in terms of current draw.

Also, to add to your first comment, I was riding with the lights on Low. I understand that the charging system puts out more when the switch is on Hi, but not on Low.

My next course of action would appear to be....

1 - Bypass the light switch so that the night time charging is on permanently.

2 - Buy LED lights.

3 - Buy a 3-phase coil and rec/reg upgrade.

Have I missed anything?

Unfortunately, the extra shipping and customs charges means buying the upgrades would be a few hundred pounds. I’m riding the 350 and doing a 250 up at the same time but i’m now concerned that both bikes will need these upgrades. It’s a bit deflating in fairness.
 

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you have found no unusual power drains.
you found the charging system is working.

to me it still sounds like a bad battery. I would have it load tested.
 

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If you have a modern Regulator/Rectifier you don't need to go the FULL led route.

I didn't and I have no issues with charging.
I do have LED:
Brake/Tail light
Rear Turn Signals
Indicator Bubs

I didn't do the Front Turn Signal (YET) and actually that allows enough current to flow that the Indicator bulb for the Turn signal doesn't need the diodes.

I DO have the H4 Halogen Headlight but that was added later as I wanted more light on the road.
 

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Discussion Starter · #16 ·
jd50i - I’ve just run the starter and measured the battery voltage. It started at 12.8V and immediately dropped down to 9.5V for a split second, but settling on 10.1 - 10.2V. After half an hour the voltage had risen to 12.6V

I also tested the current draw with the key in ON and kill switch in OFF and got 0.2A which must be the neutral bulb.

Yendor - I’m going to see if I can find a UK supplier for LED bulbs and replace them in stages, as i won’t be able to switch them all out in one big hit.
 

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Discussion Starter · #17 ·
Also, it takes a bit of cranking to get the bike to start. I wonder how much the starter drains the battery, and if only using the kick may have some effect?
 

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I would suspect the battery at this point.

10.2 V is way too low. No way your charging system can charge it up quick enough before the bike dies.

Replace the battery with an AGM (Activated Glass Mat) type which are more reliable and will also last longer than regular acid batteries.


EDIT - I just confirmed that AGM is actually Absorbent Glass Mat by the way not "Activated" LOL
 

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I would suspect the battery at this point.

10.2 V is way too low. No way your charging system can charge it up quick enough before the bike dies.

Replace the battery with an AGM (Activated Glass Mat) type which are more reliable and will also last longer than regular acid batteries.
+1

10V is very low for a battery to spend any significant time. It's not unusual to see drops into this range when you're cranking the electric start, but it should immediately jump back into the 12v range when you release the button.

I think your battery is dead/dying.
 

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Discussion Starter · #20 · (Edited)
Thanks for the advice 76TWIN and Sonreir!

I’m not sure if i’ve properly explained myself, so just to confirm, the battery dropped to, and stayed at, 10.2V WHILST the starter was cranking (only flashing up 9V on the MM for a split second the instant the button was pressed). As soon as the starter stopped cranking, the voltage rose up to 12V straight away. I repeated this three times and got the same results. Finally, after testing, it has settled at 12.6V.

The battery was bought about 6 months ago. It’s probably only done thirty odd miles tops. It’s a cheap SLA battery that came in a box with a bottle of acid I had to squirt into the holes. I did want a Motobatt but i ended up being a tight sod.

Do you think it’s still at fault?
 
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