Motorcycle Forum banner
1 - 20 of 82 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter · #1 ·
Hi there, I've bought an 1982 Honda CBX 125 (made in Italy) with some electrical problems last year. In my free time I've restore the entire bike: 12V conversion with 350 stator, new electrical system design by me, graphics ecc, the electrical issues are made by stator who burn old rectifier, ignition condenaer and the old bulbs, now electric parts are ok, it recharge correctly the battery and the engine works well in every RPM.

Now I have a sigle problem, the bike at high revs doesn't have power, in first and second gears the bike run very well at every revs, after third gear the bike turn 9000 Revs/80 km/h very slowly (only in a long road), in 4 gear it is stable at 6000 Revs, 80 Km/h, and when I put the 5 gear the bike lose Revs... Now, I've searched everywhere for the same issue and I can't find nothing, the carburator is ok with correct calibration, same with valves adjustement and ignition timing, spark plug is new, cleaned air filter ecc.

Before somebody ask, the ignition coil is the original with 2 one Ohm resistance in series and it made a good spark.

The strange thing is that the bike behaves correctly at all revs, without noises deriving from a carburetion or electrical problem, the problem occurs only from third gear onwards.
Before opening the engine and checking its status I would like to understand if anyone has had the same problem or any advice.

Thank you very much
 

·
Registered
NRA Life Member
Joined
·
1,708 Posts
Well does it have a mechanical advance, or electronic advance.

the timming you say is fine, but you have a more advanced timming at those higher rpm's.. if its mechanical, and ran off the camshaft. Remove the cover and make sure the weights are freely moving, and the springs are still tight and responsive.

If its a electronic advance, then your issue is within the cdi/tci. on the older bikes the only thing the electrical TCI/CDI functions were to control the electric timming advance. thats quite litterally its only job. all other componets to the bike were self sufficient.

So I recomend you inform us of what timming advancing system is being used. The only cbx i have ever known is not a 125cc, so if you have the manual, share it with us as well.
 
  • Like
Reactions: -Nate

·
American Legion Rider
Joined
·
26,026 Posts
Why can't it just be out of ponies? He doesn't say anything about speed or I missed it.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #5 ·
Well does it have a mechanical advance, or electronic advance.

the timming you say is fine, but you have a more advanced timming at those higher rpm's.. if its mechanical, and ran off the camshaft. Remove the cover and make sure the weights are freely moving, and the springs are still tight and responsive.

If its a electronic advance, then your issue is within the cdi/tci. on the older bikes the only thing the electrical TCI/CDI functions were to control the electric timming advance. thats quite litterally its only job. all other componets to the bike were self sufficient.

So I recomend you inform us of what timming advancing system is being used. The only cbx i have ever known is not a 125cc, so if you have the manual, share it with us as well.
if you mean the contact breakers yes, they seem ok with 3 / 4mm calibration as per manual, if you do not mean other adjustments that I am not aware of (besides the advance of the contact breakers).
I enclose the complete manual that is the same for all CB 100/125

cb125s MANUAL

thanks a lot

Maybe the engine is too busy making electricity.
Did it ever work good?
Since I bought it no, the electrical system is new and sparkles well, the coil measures electrically well and the 12V is constant

Why can't it just be out of ponies? He doesn't say anything about speed or I missed it.
I think I don't understand, but if what you mean is speed I think I wrote it in the first post
 

·
Registered
NRA Life Member
Joined
·
1,708 Posts
I suggest you go to page 10 breaker points and ignition timming. Aslo double check the valve clearances when the engine is cold and confirm these are withing spec.

Also do page 16 testing for compression. it will need 170Psi for power, and the les it has the less it will produce any power. if it gets to a 130psi, it will barely run.



The bike is at new only capeable of 79.5mph, that being said with the age and mileage of the thing, I would be suprised if it gets anywhere near that anymore. Piston and rings, the cylinder, the valves are probable to have some wear, and will not performs as it would when new.

 

·
Registered
Joined
·
38 Posts
Discussion Starter · #8 ·
I suggest you go to page 10 breaker points and ignition timming. Aslo double check the valve clearances when the engine is cold and confirm these are withing spec.

Also do page 16 testing for compression. it will need 170Psi for power, and the les it has the less it will produce any power. if it gets to a 130psi, it will barely run.



The bike is at new only capeable of 79.5mph, that being said with the age and mileage of the thing, I would be suprised if it gets anywhere near that anymore. Piston and rings, the cylinder, the valves are probable to have some wear, and will not performs as it would when new.

the first thing I have to do is to calibrate the contact breaker properly as I have only adjusted the distance of the contacts and the position of the advance, not referring to all the correct procedure, I have already looked at the valves and they are perfectly calibrated.

anyway yes, I am waiting for the instrument to measure the pressure and I too fear there are worn rings together with the cylinder, I also think the valve springs have worn out and no longer hold enough, especially at high revs.

I agree with what you think but before opening the engine (and the wallet) I wanted to check that everything else is in order, as I think it is strange that up to the second gear the engine is brilliant to rev up and only from the third gear does not have strength, I understand that it may have less power but so a clear detachment from one gear to another could affect other problems

Thank you

What is the battery and what electric accessories are running off it?
at the moment to do tests and exclude everything I only have the ignition coil and the battery connected
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #9 ·
the bike appears to have 28000 km (17398 miles) but the old owner wasn't sure as the speedometer may have been changed
 

·
Registered
NRA Life Member
Joined
·
1,708 Posts
If the points and timming are not set 100% proper, you will not get a full ignition to advance at the correct times. this will give you the exact issue you claim to have.

Ignition timming will advance as rpm increases, so even if you hav it a slight amount off, it will run ok at low rpm ranges, and fall flat at higher ones. so the points gap, and the timming plate is 100% crucial to full engine ability..
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #11 ·
If the points and timming are not set 100% proper, you will not get a full ignition to advance at the correct times. this will give you the exact issue you claim to have.

Ignition timming will advance as rpm increases, so even if you hav it a slight amount off, it will run ok at low rpm ranges, and fall flat at higher ones. so the points gap, and the timming plate is 100% crucial to full engine ability..
correct me if I'm wrong but if from neutral to second gear I reach any rev range without a problem it could still be a timing problem and therefore the engine having a wrong advance does not have the strength to push the longer gears causing the problem? or should I also have it in neutral? the bike could override without problems up to second gear and it does not make strange or empty noises ...
 

·
Registered
Joined
·
3,617 Posts
...
at the moment to do tests and exclude everything I only have the ignition coil and the battery connected
Ya but what's the battery? You must have changed it when you converted to 12 volt

... and do you figure 6 volt ignition coils with the original resistor wire set is now correct for double the voltage? Is your battery getting nice and hot?
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #13 ·
Ya but what's the battery? You must have changed it when you converted to 12 volt

... and do you figure 6 volt ignition coils with the original resistor wire set is now correct for double the voltage? Is your battery getting nice and hot?
obviously yes, a 12V 2.3ah and the regulator recharges it correctly at 14.5V and yes the ignition coil is correctly adapted to 12V, there are those who use it without the 2ohm resistors and it works the same with 12V, the only difference is that it inevitably wears out faster, the battery only acts as a "stabilizer" and the bike works equally without it, in all cases it remains cold
 

·
Registered
Joined
·
3,617 Posts
obviously yes, a 12V 2.3ah and the regulator recharges it correctly at 14.5V and yes the ignition coil is correctly adapted to 12V,
...
How did you do that, change the number or size of the windings in the ignition coils with the switch to a 350 stator, which I assume is the stator plate off a CB350 engine. or did you put a CB350 ignition setup on there, I would imagine they are different.
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #15 ·
How did you do that, change the number or size of the windings in the ignition coils with the switch to a 350 stator, which I assume is the stator plate off a CB350 engine. or did you put a CB350 ignition setup on there, I would imagine they are different.
then, the adaptation consists only in adding the 2 Ohm of resistance from what was said by those who made this conversion, there is also a well-structured online guide that I attach in the post, the stator instead is that of the 350 which has the same measures but has more dedicated windings and develops (if I'm not mistaken) 200w total unlike the original one which develops 125w
 

Attachments

·
Registered
Joined
·
38 Posts
Discussion Starter · #16 ·
tonight I had little time but I did some tests, before disassembling the whole bike and carrying out the ignition time adjustment perfectly I tried to move the contact breaker plate to anticipate a little more than what was set and in fact now the third gear can be pulled better than before, fourth gear is always bad but certainly better than before.

unfortunately I was unable to make a video as it was already dark and would not have been very useful

I then adjusted the ignition correctly and precisely as per the manual, calibrating the contact breaker plate with a precise reference to the mark on the stator, when the light bulb that was positioned lights up (I enclose the reference page).

from the original the spark plug is not resistive and not knowing it (verifying the compatibility of the one used by the original bike) I mounted one
Denso X24ESR-U, I looked under advice if the spark plug cap was also resitive and it is, I read that resistive spark plug + resistive spark plug cap creates problems, so I found in the garage a spark plug cap without resistance (measured the Ohms to be sure ) and I mounted it.

For the moment I leave the resistive spark plug and see how the bike goes.

I hope tomorrow to have more time and try the bike in this configuration, perhaps by making a video on board
 

Attachments

·
Registered
NRA Life Member
Joined
·
1,708 Posts
tonight I had little time but I did some tests, before disassembling the whole bike and carrying out the ignition time adjustment perfectly I tried to move the contact breaker plate to anticipate a little more than what was set and in fact now the third gear can be pulled better than before, fourth gear is always bad but certainly better than before.

unfortunately I was unable to make a video as it was already dark and would not have been very useful

I then adjusted the ignition correctly and precisely as per the manual, calibrating the contact breaker plate with a precise reference to the mark on the stator, when the light bulb that was positioned lights up (I enclose the reference page).

from the original the spark plug is not resistive and not knowing it (verifying the compatibility of the one used by the original bike) I mounted one
Denso X24ESR-U, I looked under advice if the spark plug cap was also resitive and it is, I read that resistive spark plug + resistive spark plug cap creates problems, so I found in the garage a spark plug cap without resistance (measured the Ohms to be sure ) and I mounted it.

For the moment I leave the resistive spark plug and see how the bike goes.

I hope tomorrow to have more time and try the bike in this configuration, perhaps by making a video on board

LOL, good your making some progress, but I had a feeling the ignition was not in propper spec/adjustment.

Also good catch on the plug boot combo(y)
 

·
Registered
Joined
·
38 Posts
Discussion Starter · #18 ·
Unfortunately, given the rain of the past few days, I tried the bike this afternoon after the advance setup etc. but the bike still doesn't have power, in the end it behaves more or less as before, I also made some videos but they are useless considering what I later discovered.

A friend of mine has recovered tonight (here it is 9:00 pm now) the tool to measure the cylinder pressure and yes, problem found, 75 PSI instead of 175 PSI, in the next days and / or weeks I will proceed with the opening of the engine and checking the cylinder and head, I hope to get by with little expense.

Thanks to all of the valuable advice
 

·
Registered
Joined
·
3,617 Posts
Why not one day, :unsure: shouldn't take much longer then that to tear it down, it's just a little motorcycle,
but you are going to need a small torque wrench before you can re assemble it properly if it's not just a valve clearance adjustment. I would adjust the valve clearances first and then compression test again if valves appear out of adjustment, that might save you a lot of work.
 

·
Registered
Joined
·
3,617 Posts
... hey wait, this is a 2 cylinder motorcycle, 75 PSI instead of 175 PSI in one cylinder, what's the other one? or was one 75 and the other one 175 psi
 
1 - 20 of 82 Posts
Top