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Discussion Starter #1
Hi all, well my wifes little cb100 wont kickstart now. it was working great and has slowly gone down hill. First when it wouldn't kickstart I could put it in gear and hold the clutch, run with it and then release the clutch and it would start, now nothing. Before I go ripping into anything any suggestions on where to start? Also would this bike be a 12v system? I also have a 71' cb350 and the battery is dead so when I want to start it with the electric start i hook it up to my civic (without the car running) and it turns over like a charm. I this with the cb100 and barely put the clamps on the bike and started to see a little smoke. I fear I have fried something! Any help with these two issues would be greatly appreciated. Thanks guys!
 

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Independent M/C Shop
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Your Honda CB100 has a 6v system and that's why you saw smaoke. Most likely you fried many of the electrical components as well. If the bike won't start, check the simple and inexpensive things first. Try a fresh sparkplug and see if there is a good spark. If not, your problem is with the ignition system. First thing to check is the points and condenser located at the top of the engine on the left side. You may find an oil film on the contacts of the ignition points (which is fairly common on older machines) and you will have to clean it off with electrical contact cleaner and a plain (not glossy) business card. If the points are little pitted, you'll have to file them flush with a fingernail file and then clean as outlined above. Then you have to set the point gap to spec which is between .012" to .016" with a feeler gauge. You then have to check and set the timing. The left engine side cover has an inpection port of sorts that you will remove and see timing marks. The "F" mark is when the points just start to open and "T" is Top Dead Center when the T is lined up with the timing mark. Use a buzz box across the points to tell when the points just start to open when the "F" mark lines up with the timing mark. The buzz box simple makes a buzzing sound going across the points when they are closed and stops abruptly when the points open and break the circuit. This makes the adjustment easy because you can listen to waht is happening with the points while you are watching the timing marks while rotating the engine by hand. Adjust the points accordingly until the buzzer stops at just the right time as the "F" mark lines up with the timing mark. Your points and ignition timing are now set. Of course I should have mentioned that you should check and make sure your camchain has no excessive play in it first. While you are at it, you can line up the "T" mark with the timing mark and adjust your valves. Rotate the engine and watch your intake valve open and then close. Then watch the timing marks and line up the "T" mark. The valve lash can then be adjusted. Honda Specs are .002" for both intake and exhaust on the CB100. By the way, The spark plug for your bike is an NGK D-8ES and the spark plug gap is .025" to .028" and if you want to make a compression check, hold the throttle all the way open while you rapidly kick the engine (about 4 or five strokes of the kick starter) while you have a compression gauge mounted in the spark plug hole. The dry compression should be between 115 to 170 psi to be within Honda specs. If the compression is lower, try squirting a bit of oil through the spark plug hole and reinsert the compression gauge. Now try the test again. This is a "wet" compression test. If the compression reading stays the same, check you valve adjustment again as the valves may be too tight. If the valve lash is correct, you probably have a bent valve. If the compression reading has shown a significant increase, you probably have severely worn or broken piston rings and/or piston. OF course, before you get into all of this, see if you are getting a good supply of fuel to the carb from the tank, check your engine oil level, and again the spark. If you have fuel & air, compression, and spark (all at the proper time) the bike should fire up. Hope this helps. I used to be a Honda mechanic and service manager. I've worked on many of these machines over the years and I absolutely love them. If you have no luck, decide to give up on it and want to get rid of it (and you are in or near New England), PM me and let me know what you might want for it.
 

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Discussion Starter #3
Wow, thanks so much. I'll start with all that. I kind of have a feeling that it could be as simple as the petcock/fuel line may be clogged. But thanks for all the steps and advice. I do have one further question...

Assuming i did fry the electronics, how can i test to see what is still good and what needs to be replaced?
 

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Independent M/C Shop
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If you fried something, most likely it was the battery, and if that was giving you problems which is what warranted you to try and jump it, it was probably trashed anyway. Those little batteries never last more than a couple of years before they should be renewed. Start with a fresh battery (they are pretty cheap for that size). The correct battery you need is a 6N6-3B and when you first get the battery and it is freshly filled with acid, put the battery on a trickle charger for a few hours before installing in the bike. Also make sure that the battery is only filled no higher than the high level mark in each cell with the acid (the batteries you buy at Wal-Mart require you to fill them with acid yourself). See if you have spark with the new battery. You might want to check the rectifier to make sure it didn't get zapped. Use an ohm meter to check continuty between the following leads - You should read good continuty one way and absolutely no continuty in the opposite direction when you switch the leads around. If you have continuty in only one direction, your rectifier is still good. If you get continuty in BOTH direction across any of the wires tested the rectifier is bad and must be replaced. If you have no continuity across both directions of any of the wires tested, the rectifier is bad and must be replaced. First - disconnect the rectifier at it's plug. Then go across the following wires with your ohm meter as I mentioned above. (1) test across the green and pink leads in both directions. (2) test across the pink and red/white leads in both directions. (3) test across the green and yellow leads in both directions (4) test across the red/white and yellow leads in both directions.
I doubt you fied your ignition coil, but if you did, it requires a specialized piece of test equipment - you would have to take the ignition coil to a bike shop and have them test it for you. I wouldn't worry about this though unless you've tried everything else I mentioned earlier and you're not getting any spark. Since you only touched the terminals briefly with the 12V, It probably wasn't long enough to melt down your wiring harness, but it wouldn't hurt to check it out visually to see if there is any obvious damage. BTW - If you purchase a new battery - try to get a Yuasa brand. It's the best quality battery that will return the best performance and longevity in your machine (in my opinion).
 

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Discussion Starter #6
Thanks Downeast Thunder. Very Helpful so far. This weekend I will switch out the battery. To check for spark with the new battery i will have to have my wife kickstart the bike while i hold the plug against the metal, right?

The bike ran just a few days before. We had gone for a ride around town and stopped for like an hour. When we went back to start the bike up it wouldnt kickstart, however i could push start it while popping the clutch. About three or four days later that wouldn't work either.
 

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With the spark plug out and connected to the spark plug wire and the electrode end laying against the head, you can easily crank the kickstarter b y hand and watch for a spark on your own. Just remember to have the engine shut off switch in the run position and the key on. Have you already checked your fuel system yet? Make sure your engine oil level is at the proper place on your dipstick too. CB100's don't hold very much oil to begin with and you have to check it on a regular basis (probably not the source of your problems but it just came to mind to remind you of this on this particular machine).
 

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Thanks Downeast Thunder. Very Helpful so far. This weekend I will switch out the battery. To check for spark with the new battery i will have to have my wife kickstart the bike while i hold the plug against the metal, right?

The bike ran just a few days before. We had gone for a ride around town and stopped for like an hour. When we went back to start the bike up it wouldnt kickstart, however i could push start it while popping the clutch. About three or four days later that wouldn't work either.
I have a CB,and they are so simple that I can almost guarantee that it is your battery. Really, the only thing you should ever do is charge [with a battery charger and SLOWLY] or replace a battery. You should never try to charge up a low battery using the bike. You could easily fry a part that costs many times what a new battery costs. Jump starting is bad as well--of course about the only thing you can jumpstart it with would be an old 6 volt farm tractor---
 

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Discussion Starter #9
im going to replace the batter and check for spark first off. The next thing I was going to go through was the fuel system. it seems simple enough, but would you start at the carb or petcock? I mean was going to pull the fuel line off at the carb and see if i get a good flow out of it. If I do could there be a carb adjustment? The last week my wife was able to ride the bike she said it was making a weird noise, like it was bogging down about to die but then would pick back up. I don't know why I didn't think to mention this before...does that little info help narrow anything down. Im gonna be working on the bike tomorrow (saturday).
 

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Don't touch the carburetor until you've run through all the checks and have diagnosed the carburetor as being your problem. You can disconnect the fuel line at the carb and turn on the petcock to see if you have a good flow fuel as a quick check. If not you can drain the tank, remove the petcock and flush both tank and petcock. Also check your fuel cap because it is supposed to be vented to atmosphere. Sometimes the cap vent gets clogged and ceates a vacuum in the tank which hinders good fuel flow (and can completely stop it in some cases). I don't think this is your problem though. Most likely your battery crapped out. It's possible to run these machines with a dead battery from the cahrging system, but you have toi keep the revs way up to do it IF you can get it running in the first place. Why? Because the CB100 does not employ a magneto or "energy transfer system." The CB100 uses a "battery-coil" ignition system and requires a good battery in order to run properly. When the battery starts to go bad, it causes all kinds of operational problems. Just hpe you didn't zap your selenium rectifier when you tried jumping the system with a 12V battery. My advice is to try the new battery first (you need one anyway) and if that does not make your bike happy, get hold of me and I'll help you out from there.
 

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Hey Downeast thunder. I know this thread is old. You said the 1973 does not have a magneto. I have a 1970 and i think it does have a magneto.

Did they get rid of the magneto after 1972?
 

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None of the CB100's or CB125's of any year ever used a magneto of any kind - they all used battery/coil ignition systems. The 1970 model CB100 uses a battery/coil ignition system. What you think is a magneto is a stator and is part of the charging system & has nothing to do with the ignition system. This applies to all CB's, CL's, and SL's.
 

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Thanks for that info. I have a 1970 that the brake light comes on while riding and then it will die at a stop. I read somewhere that said if the brake light stays on it could be a sign your charging system is not working. Have you heard of that? Sorry for the bad typing as I am on my phone
 

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Good to see you back here,DownEast... I thought it was very unfortunate a while back when someone on this forum said stupid things about bike shop owners. Rest assured that you are valued by guys here who really want to learn about bikes.
 

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another fried cb100

I recently purchased a cb 100 that had been laying around in a
barn. The last time anyone recollects the bike running was '91.
A helpful grandson of the owner wanted to show me it would
run by jumping it from his car and spraying ether. Indeed it
did start, but I got a sick feeling when I noticed all of the lights
come on and then simultaneously dim out. At that time I was
not aware that this was a 6-volt system. Well, I did get a new
battery, and after a little cleaning & tweeking the bike runs
fantastic. However, none of the lights work. I looked at a few of
the bulbs and they do not appear to be burnt.
So.... my question is: Is there a fuse or fusable link that protects
the system? or Where do I begin to look for the damage and what
do you suspect I need to replace to get the lights working. My wife
would like to use it as a local commuter/grocery getter before the
season ends.
 

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So.... my question is: Is there a fuse or fusable link that protects
the system? or Where do I begin to look for the damage and what
do you suspect I need to replace to get the lights working. My wife
would like to use it as a local commuter/grocery getter before the
season ends.
My CB550 has 3 fuses on the opposite side of the battery. There's a little black rectangular cover that pops right off to reveal them. The box says something like "headlight 7.5A, taillight 5A, main 15A" or something similar. I know it's not the same bike, but a lot of these bikes will have similar systems for this kind of thing.
 

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I have a CB125S also.. just trying to get it running. any chance it would have any spark without a battery? If I hold onto the spark plug I get a little shock.
 
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