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Discussion Starter · #1 ·
Hey guys,

Engine has been rebuild recently: carbs, cylinders, head, new condenser, new coil, air filter foam rebuild, ... Rides beautifully although the bike never gets to it full potential it seems. 5th gear WOT just doesn't seem right, I get up to 70km/h and the bike does a lot of hiccups. It feels like it wants to go but it just doesn't.
Are those symptoms of a slipping clutch? The plates still have enough meat on them and the clutch has been adjusted by a pro... Enough play on the lever etc.

Carbs aren't yet perfectly adjusted though. Idle circuit is dialed in, float level is stock, needle is one slot higher than stock (which helps), stock jets.

Haven't checked the color of the plugs after shutdown at WOT yet. Could it be the main jet?

Any insights?
 

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Only after you do a series of plug chops can you say for sure about the jets.

Have you checked your ignition, including the advance?

Can't positively eliminate the clutch, but, not likely.
 

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Sensei
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Let's see.....70 kph is about 46 mph, so on a bike that SHOULD top out about 60+ mph (90/95 kph) you SHOULD be JUST shifting or have just shifted into fifth at about 68/70 kph.....

Run the gears out....1st 0 to 25/27 kph, 2nd to 43/45 kph, 3rd to 50/52 kph, 4th to 68/70 kph, then fifth ...(once it's broken-in)

If you are only running at 70% of possible revs, expect at best 70% of top speed.......
 

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Discussion Starter · #4 ·
Only after you do a series of plug chops can you say for sure about the jets.

Have you checked your ignition, including the advance?
Ignition timing is set so the bike picks up nicely when revving. Although the revs don't fall back all that quick, they tend to linger a little bit.

I'll do the plug tests once the rain settles over here.
 

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Discussion Starter · #5 ·
Let's see.....70 kph is about 46 mph, so on a bike that SHOULD top out about 60+ mph (90/95 kph) you SHOULD be JUST shifting or have just shifted into fifth at about 68/70 kph.....

Run the gears out....1st 0 to 25/27 kph, 2nd to 43/45 kph, 3rd to 50/52 kph, 4th to 68/70 kph, then fifth ...(once it's broken-in)

If you are only running at 70% of possible revs, expect at best 70% of top speed.......
That wouldn't explain the hiccups at "full" speed would it? It tends to hiccup in any gear when I'm close to WOT.
 

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Sensei
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Hey guys,

Engine has been rebuild recently: carbs, cylinders, head, new condenser, new coil, air filter foam rebuild, ... Rides beautifully although the bike never gets to it full potential it seems. 5th gear WOT just doesn't seem right, I get up to 70km/h and the bike does a lot of hiccups. It feels like it wants to go but it just doesn't.
Are those symptoms of a slipping clutch? The plates still have enough meat on them and the clutch has been adjusted by a pro... Enough play on the lever etc.

Carbs aren't yet perfectly adjusted though. Idle circuit is dialed in, float level is stock, needle is one slot higher than stock (which helps), stock jets.

Haven't checked the color of the plugs after shutdown at WOT yet. Could it be the main jet?

Any insights?
Does the needle sit higher (clip moved down) or did you lift the clip (dropping the actual needle)?
My REAL question is: With everything else "stock", why did you change the needle? (and HOW does it "help"?)
Air filter Foam oiled or dry?
 

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Discussion Starter · #7 ·
Does the needle sit higher (clip moved down) or did you lift the clip (dropping the actual needle)?
My REAL question is: With everything else "stock", why did you change the needle? (and HOW does it "help"?)
Air filter Foam oiled or dry?
Clip is higher so needle sits lower. I did that to eliminate the hiccups at mid range throttle, they are gone now.

The foam is dry, no oil at all.
 

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Sensei
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Both those things usually tend to lean out the mixture, dropping the needle definitely does ....However, if the new filter is more restrictive than the original, then the needle change makes sense....What do the plugs look like?......
My previous question should have been "What ELSE did you change from stock that it required dropping the needle at all?"...... The bikes ran fine from the factory with ALL the standard settings.....Whatever you changed caused the detrimental effect.......
 

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Discussion Starter · #9 ·
I got some thing mixed up from the start. The needles were in the stock position. They are now too. The plugs look to be too lean but not like super duper lean. Just a tad bit on the lean side. Do you think oiling the air filter foam will accommodate for that?

I also noticed today the engine wants to stall when the lights are on. I switched to 6v led lights some time ago to reduce the draw from the charging system. Bad stator maybe? I haven't done the stator mod that's a sticky on this forum yet, is that something that's recommended to do?
 

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My previous question should have been "What ELSE did you change from stock that it required dropping the needle at all?"...... The bikes ran fine from the factory with ALL the standard settings.....Whatever you changed caused the detrimental effect.......
Not that it necessarily applies here, but do you think that fuel available today might affect how a 50 year old bike runs, even on completely stock settings ?
 

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Let's see.....70 kph is about 46 mph, so on a bike that SHOULD top out about 60+ mph (90/95 kph) you SHOULD be JUST shifting or have just shifted into fifth at about 68/70 kph.....

Run the gears out....1st 0 to 25/27 kph, 2nd to 43/45 kph, 3rd to 50/52 kph, 4th to 68/70 kph, then fifth ...(once it's broken-in)

If you are only running at 70% of possible revs, expect at best 70% of top speed.......
CB 125 is not a strong bike. You need to rev it high to get proper speed, otherwise You wont get max speed.

I have had hiccups problem two years ago at exactly the same speed. Try to switch front lights off... It was remedy for this problem and it was bounded with interminent charging problems in my bike. I was not able to increase rpm at 5th gear above 70 km/h.
 

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Sensei
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Not that it necessarily applies here, but do you think that fuel available today might affect how a 50 year old bike runs, even on completely stock settings ?
Richard, I agree, but if anything he should have be adjusting slightly richer rather than leaner for modern fuels........

Plus, a picture of the bike would help because we did not get a 125 (twin or single) with a K5 designation.....
I don't even know what specific bike we are discussing, so I can only offer generalizations based on my experiences...
Because of the two "problems with lights on " comments, I'm ASSUMING a battery ignition, but would be helpful to know for sure......
The more and better information we have, the more likely the correct diagnosis will come sooner.....
Until then, it's just best guess based on what we do know so far.....
 

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Discussion Starter · #13 ·
So after a lot of testing I have some new information...
The bike runs okay when the battery has been charged (with an external charger). After a while the battery drains I guess while riding and the bike stalls. When I turn on the lights it does this as well. I know it's not a strong bike but it should run smoothly though. The bike is a Honda CB125 K5 twin. 6V system. Picture included.

My guess is that the alternator is the issue, how do I check this and more importantly, how do I fix this? I read some threads about doing a mod which charges the battery at maximum capacity at all time instead of only when the lights are on. Would this be advisable? What do you guys think?
 

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Sensei
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From the pic, it is a smaller displacement version of the CB175......Pretty bike BTW.......

Before we go any further, how old is the battery?...... How long did it sit?.....
How often has it "drained" so low you had to recharge it for more than 3 hours?...
What voltage READING does a voltmeter produce when connected to the battery with key off?
What is the battery's amperage?
At what rate (how many amps) are you recharging it?....
 

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Discussion Starter · #18 ·
It's a K5 model for Germany indeed. The battery is one year old, possibly been drained a few times. I'll check the voltage readings in a minute.
 

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So after a lot of testing I have some new information...
The bike runs okay when the battery has been charged (with an external charger). After a while the battery drains I guess while riding and the bike stalls. When I turn on the lights it does this as well. I know it's not a strong bike but it should run smoothly though. The bike is a Honda CB125 K5 twin. 6V system. Picture included.

My guess is that the alternator is the issue, how do I check this and more importantly, how do I fix this? I read some threads about doing a mod which charges the battery at maximum capacity at all time instead of only when the lights are on. Would this be advisable? What do you guys think?
Hello Jesper,

nice bike, looks really nice. Rear lamp and fenders proves that this is German model. I have exaclty the same model. To register this bike in Poland I had to convert rear lamp to General Export version (looks like E.T. face).

I would check following issues:
1) battery voltage level (should be 6.2-6.3 V)
2) charging voltage (it should be ca 6.7V above 3000 rpm, 7.0 V at 5 000 rpm and 8.3V at 10 000 rpm)
3) charging current (it should be ca 2A above 3000 rpm, 2.7 A at 5 000 rpm and 4.5A at 10 000 rpm with lights off)
4) rectifier connections, this is simple bridge of semiconductors.
5) connection from AC generator. It is placed in rubber bushing between left side and top cover. See pictures below. Interminent brakes in wires led to bad charging.

20170225_182024.jpg

20170227_215821.jpg

20170227_215828.jpg

I hope it will help You...
 
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