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Old 06-28-2013, 12:29 PM   #1
Woogies OP
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Little Honda is cutting out!

I thought I'd repost a problem I had earlier with some updates rather than resurrect a dead post.

I have 1974 CB125s I bought from my uncle. Very low miles. However I'm getting some weird cut offs. I'll be driving along and suddenly the bike will shut off. This happens more often as I'm coming to a stop and I pull the clutch in. I have to pull over and wait a few minutes before kicking it again. I don't notice anything out of the ordinary while driving.

Now when I bought the bike, i notice a good amount of chatter from the valves. My uncle said he did some adjusting on the valves to quiet them up. My suspicion is a valve timing problem. Anyone else have any alternative ideas?

I want to get this fixed soon, but I don't want to spend money throwing random parts at it. Also does anyone know where I can find a service manual for this thing (preferably free )
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Old 06-28-2013, 12:35 PM   #2
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make sure the battery is topped off, Older Hondas with points will do this if it isn't full or near full.
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Old 06-28-2013, 12:53 PM   #3
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Battery has been fully charged.

It is a very random issue, seems to cut out when it wants too. It isn't consistent, sometimes I can ride for 30min + before it first cuts off. But after it starts, it becomes more and more frequent.
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Old 06-28-2013, 03:33 PM   #4
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Older bikes has problems with the ethynol in the gas. Empty the gas tank put in a clear fuel filter and if possible put in gas with no ethynol. Check your gasket and hoses if it tolerates ethynol in gas.
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Old 06-28-2013, 03:39 PM   #5
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Quote:
Originally Posted by Woogies View Post
Battery has been fully charged.

It is a very random issue, seems to cut out when it wants too. It isn't consistent, sometimes I can ride for 30min + before it first cuts off. But after it starts, it becomes more and more frequent.
OK, that is needed information. I would try measuring the resistance in the coil then it sounds like the coil is getting hot and failing. Can also be a issue with the battery terminals. Just because the battery is new, or just topped off doesn't mean much.....so test the connections first, then test the resistance of the coil. I would just yank the tank too and make sure all the electrical conns are tight.
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Old 06-28-2013, 03:40 PM   #6
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Older bikes has problems with the ethynol in the gas. Empty the gas tank put in a clear fuel filter and if possible put in gas with no ethynol. Check your gasket and hoses if it tolerates ethynol in gas.
But would that not be a full time running issue? Sounds electrical to me.
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Old 06-28-2013, 03:44 PM   #7
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Here's a little list of what goes wrong on these old Honda singles,

Plug gets old and needs to be replaced, gunk in tank makes them run good and bad intermittently, Coils go bad or have a bad connection leading to intermittent running issues, points go bad, but that is usually a full time running problem, battery is bad and won't hold voltage or current, coil has a heating up problem. That is about it unless it is rectifier/regulator related. Or the other thing but rare, key switch/kill switch is going bad.
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Old 07-03-2013, 02:29 PM   #8
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Originally Posted by Sniper X View Post
Here's a little list of what goes wrong on these old Honda singles,

Plug gets old and needs to be replaced, gunk in tank makes them run good and bad intermittently, Coils go bad or have a bad connection leading to intermittent running issues, points go bad, but that is usually a full time running problem, battery is bad and won't hold voltage or current, coil has a heating up problem. That is about it unless it is rectifier/regulator related. Or the other thing but rare, key switch/kill switch is going bad.
I'll check the coil for sure and swap the plug. Does anyone know the recommended resistance of the coil?

As a side note, while we are talking about electrical stuff and the rectifier.... there is a unusual amount of voltage fluctuation while riding. For example, when I use the turn signals the headlight will dim significantly and even flash slightly with the turn signals.
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Old 07-04-2013, 11:13 AM   #9
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Well I finally started getting my hands dirty today. I had quite a surprise when I found that it had absolutely NO air filter. So that's first on the repair list. I might just swap the coil and plug as well, then see if that solves the issues.
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Old 07-04-2013, 03:28 PM   #10
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i have a CB100 and it did something like this,, had been sitting for 30 years in the back of my place of work, good thing is it was serviced and tank drained before it was stored, had a new 30 year old plug in it. that was the cause of it's problems.
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Old 07-08-2013, 08:55 AM   #11
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i have a CB100 and it did something like this,, had been sitting for 30 years in the back of my place of work, good thing is it was serviced and tank drained before it was stored, had a new 30 year old plug in it. that was the cause of it's problems.

Well, I'm changing out the plug, coil and putting an air filter in. Hopefully one of these will fix it! Thanks for the suggestions guys!
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Old 07-13-2013, 07:30 AM   #12
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So I changed out the coil, plug and filter yesterday. Didn't seem to fix it.

In fact, I'm writing this post sitting next to my bike on the side of the road.

I've been driving for about 30min when it started happening. I can tell right before it happens. Throttle looses responsiveness and finally has no affect at all. I pull in the clutch and that's it, the bike shuts off. I have to pull over, wait 10-15min before it'll start again. With a couple miles it'll do it again.

Any other ideas?
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Old 07-13-2013, 09:10 AM   #13
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Tank vent is clogged? After 30 minutes riding there is enough vacuum in the tank to keep fuel from flowing into the carburetor. Over the 10-20 minutes you wait for it to start again, a little air goes into the tank allowing fuel to go into the carburetor.

If it were an electrical issue the throttle wouldn't lose responsiveness.
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Old 07-16-2013, 08:31 AM   #14
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Tank vent is clogged? After 30 minutes riding there is enough vacuum in the tank to keep fuel from flowing into the carburetor. Over the 10-20 minutes you wait for it to start again, a little air goes into the tank allowing fuel to go into the carburetor.

If it were an electrical issue the throttle wouldn't lose responsiveness.
I'm not sure whether this has a vented gas cap or not, but I replaced it a few months ago because of leakage (still leaks anyways )
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Old 07-16-2013, 08:35 AM   #15
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Fuel flow issue?
And check the valve lash, they get tight when they get hot...
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