Author Topic: Well hello!  (Read 294 times)

Offline Ko En

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Well hello!
« on: July 03, 2018, 12:59:08 AM »
Hello from a slightly desparate recent Honda enthusiast.

First of all, I have a little CB125j 1978, no cb750 as most on this forum seem to have (or is that the wrong impression?), so I am not sure if I qualify. Single overhead crazines yes. only 125cc's though.
To make my commute more fun I have bought a cb125..... hahaha
No real experience with motors, I didn't have a cbt yet, bought it on eBay and had it delivered. Arrived and even though I was over the moon, I didn't really know how to start it or change the gears... read the owners manual, got my CBT, great fun.
It was running quite rich though and the big heaps of smoke following me around, people desperately overtaking me and pinging sounds lead me to believe there was an issue. When it started to stall I blamed it on overheating. Adjusting the floats after carb cleaning fluid in the petrol helped to make it run lean. But there was still oil on the spark plug...
I took the engine off, it sat in my garden for two weeks while I studied all I could find (Haynes, fora) about the engine and got started on it. I had imagined that the valve seats were leaking and indeed the o-ring under the intake valve was pulverised. There was literally a pool of oil on the piston. The pistons were caked, piston head also and I spent many hours cleaning/polishing them. Got one of those suction thingies with the grinding paste, voila.
The sides of the cylinder wall looked smooth and as the bottom part of the cylinder didn't come off at all I left it at that.
I put it back together, made a few mistakes... but in the end got it in one piece. It worked! that feeling.... prouder than a monkey with three dicks.
That feeling didn't last long. Although it did pass the MOT and I could ride it to work it started cutting out after a while... new points, timing set, gap set, valve clearance re-set. still hiccuping after 5 minutes of riding, or sometimes just flop dead. New condenser, same problem, new coil... same problem.
I love that little bike, makes me happy, people smile at my when I pass them on my orange machine.. but my problem is, I don't have a place to work on it, I do it on the sidewalk in front of my house in the evenings... and I need it to get to work... Ok, bad choice to get a 40 y-o bike for commuting but I don't believe in spending money on something I'm not super excited about.
So here I am in a last call, am I overlooking something? Or would it be as simple as a leaking gasket.... I hope not, really don't look forward to taking off the engine again..
Peoples' stories on fora have helped me a lot to avoid and/or solve mistakes I made. Someone offered to buy my bike the other day, as is. He would take apart rechrome redo everything and sell it... I know I should sell it sooner or later, but I really don't want to. At least not until I have fixed it and enjoyed it a bit more.
If anyone could share some of their experience and knowledge to help me solve this "mystery" I would be more than grateful.
So, it cuts out; when it cuts out the blinkers don't work, but the normal lights do. I can normally start it by kicking with the choke on and taking it of quickly. After that it'll ride for less than a mile before it cuts out again. Normally cuts out when I am coasting. Battery seems healthy at 6.7 volts.
Any help greatly appreciated.
Cheers!


Offline haynes66

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Re: Well hello!
« Reply #1 on: July 03, 2018, 05:04:27 PM »
sounds like it could be anything or everything with a bike like that. my advice would be to put it on ebay and get yourself a runner. there are plenty out there. the cb125j is slowly becoming collectable so you should find a buyer pretty soon.
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Offline Ko En

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Re: Well hello!
« Reply #2 on: July 08, 2018, 11:15:16 PM »
Thank you for the sound advice.
In the meantime the new coil helped against the bike cutting out and I'm almost ashamed to say it, but by using the reserve setting for petrol I managed to overcome it stuttering and dying on me after one mile....(becoming the wall of shame, if it weren't already)
Increase the floats -> running great. Still very noisy though, I found out that the 'j' version has a different way of tightening the cam chain and this helps a lot. Let it idle 5000 revs and adjusted the mixture screw.. after that it ran terrific.
On day later, it starts to stutter around 5k-6k revs...
Driving me crazy.
Back to the drawing board, might be petrol delivery not great, might be retard thingy not working properly, might be I need to reset the timing after I took away all the slack from the cam chain..
A new week, let's see if it gets me to work tomorrow.

Offline Oddjob

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Re: Well hello!
« Reply #3 on: July 09, 2018, 11:11:23 AM »
Get some carb cleaner if you haven't already and start the engine, as it ticks over spray the carb cleaner around the carb area, if the engine picks up in revs you have an air leak. 40 year old bikes can suffer with O-Rings perishing. Don't spray carb cleaner on the exhaust as it's pretty combustible.

My advise would be to find someone who really understands these little engines, ask them to get it running right and then learn how to keep it running right after that. The learning curve is pretty high for a 40 year old piece of equipment although saying that I admire your willingness to have a go yourself.
Don't play stupid with me, I'm better at it

Offline matthewmosse

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Re: Well hello!
« Reply #4 on: July 09, 2018, 11:27:27 PM »
Check the filler cap is allowing air in as fuel goes out, had a mates bike go like that, would go a mile, stop, need slight choke to 're start and died again  within the mile, until the battery gave out, he asked me to help recover it, we went out to collect it, jump leads in hand, I pulled the fuel cap off, left it slightly open and it went home fine, Turned out an aftermarket filler cap was vacume locking fuel, as no pinhole to allow air in, had similar from rust clogging the filter on the fuel tap, fuel could seep past but not fast enough to keep up with engine demand, oh and the old kink in the fuel line. Often it's a simple thing that's easily overlooked.
Got a 500/4 with rust and a sidecar and loadsa bits. nice and original and been round the clock

Offline Ko En

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Re: Well hello!
« Reply #5 on: July 10, 2018, 12:30:35 AM »
Thanks for the advice.
When I blow on the cap air goes through reasonably easy. I had tried that in the past. I lowered the floats a little bit, last thing I did before it started acting up was raising them.. Tightened the carb extra, extra, tested if petrol comes through when I open the tap, it runs out just fine, also in normal position. Started it up, was hiccuping quite extreme, set the tap on reserve: all fine. Beats me.
I'll try to take out the petcock when my tank gets lower. 
Thanks again,

Offline Oddjob

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Re: Well hello!
« Reply #6 on: July 10, 2018, 12:13:06 PM »
I've seen this before, the brass pipe on the petrol tap was partially blocked, ran fine on reserve as it gets petrol from another opening in the tap. Sounds like you need to get the tap out and check for blockages.
Don't play stupid with me, I'm better at it