1975 Honda CB125S and 1981 CM200T


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Fuel is going directly into the carb currently and seems to flow fine. No tank or petcock currently to worry about. When assembling the float, I adjusted it to spec, 24mm I think. It was at 21mm before adjusting... way off.

I too was thinking the main jet may have an issue but I want to make sure the electrical system is in good shape before I break open the carb again.

Anybody know what the ohms should be on the coil?

Where do I test it’s voltage when running?

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Was the engine fully warmed up w choke fully open? (At idle it will take better than 10 minutes to get it good and warm). But I’m betting the main jet is clogged. It will idle just fine but goes super lean when you crack throttle. Or the choke wasn’t fully open and going rich cause it couldn’t get enough air.
By the way, thanks for all the tips and suggestions. I’m taking them all in even if I don’t directly respond. I really appreciate it.
Choke was open and I'll check the main jet sooner than later. In the video, the engine was not warm, but this weekend I let it get run for a good 10 or 15 minutes before adjusting the air screw to try to lean it out. The (new) spark plug was super black which is why I was thinking it was running rich, but maybe the idle was rich and when I cracked the throttle it went way lean. Once it was warm, I would barely touch the throttle and the engine would rev. If I was light on the throttle, it ran okay, heavy on the throttle and it would get very rough. Next time I get it re-assembled I'll record so you can hear it. Fingers crossed that adjusting the timing will help. I am suspicious of the electrical system as well.
Long time since an update and in the mean time... the world has changed! I hope everyone is safe and healthy. I know we’re all going through some tough times. Thank god I have an old motorcycle to work on to clear my mind from our situation. I hope each of you have the similar or another outlet. We all have our priorities and it’s not motorcycles likely, but it’s important maintain a healthy mind. Hobbies are great for that. Maybe selfish, but from here on I hope to keep this thread about these bikes.

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A lot of work has been done on the ‘75 CB125, but you’d never know it by looking at it. Mostly because work was done but not much accomplished. Frustrations were high because I could not figure out why it was running so rough and so rich. I rebuilt/cleaned the carb twice. Triple checked the air filter/air box. I re-jeted to a smaller size. I replaced the ignition coil. Nothing was working, still idled great and revved like hell. Finally my office landlord asked about the needle. I don’t know why I hadn’t tested it. I had it at factory spec, but when I lowered it one notch... the engine started running great! There is, of course, more to do on the engine, but it’s good enough for now and I’m moving forward.

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Now I’m working on the front. I’m going to rebuild the forks and clean up the rim. It has this kinda funky manual disk brake. I took it apart to clean it as well. In the process I tore the paper gasket. It appears this gasket is no longer available. What’s the best way to repair this? It’s not under pressure or heat. It seems to be just for keeping dirt out.

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I hear you Maritime and that’s in the extended plan. However, for now I’m sticking with what I got. Is it plausible to use a little “gasket maker” right where the tear happened? It’s a clean tear, no missing material.

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I ended up finding a product that was perfect for fixing old (non-critical) gaskets. It stays pliable and seems to have done the trick.
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Front brake calipers are cleaned, oiled, and rebuilt. I also cleaned and re-oiled the cable. I’m trying to reuse anything not overly broken on this bike. I actually think this brake cable is one of the few things not original on the bike, but it was there when I got it, so that counts. Repairing some of the stuff is where all the fun and frustration is at! Funny how those two go together.

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I forgot to take a “before” picture but these forks were in super bad shape. Everything has some degree of rust on it. It took an act of god to get them off the bike. I then took them apart and dipped most of the parts in evapo-rust. After lots of scrubbing they are starting to shape up.

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These forks are of the external spring variety. If you look at any stanchion from this era on eBay you will see this 4” area in the middle that is rusted. Mine were super rusted until I scrubbed on it for way too long. It happens under this plastic sleeve called the “fork spring guide”. I have no idea what it’s purpose is, but I wouldn’t expect the Honda engineers to put it there without a good reason.

Any idea what this thing does other than give moisture a good place to hang out? It slides between the spring and the stanchion and has a lip to keep it at the top.

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Full disclosure... I broke one of the sleeves/guides during disassembly so I’m deciding if it really needs to be replaced. I was actually thinking about removing it anyways to avoid future rust, but please tell me if you think it needs to be there. Also, this whole spring section gets covered by a rubber boot, FYI.

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Probably prevents wear (and noise) between the two. Get grit in the area and there could be a lot of abrasion.
Oh wow... how the time flies... I easily slipped out of the habit of keeping this thread updated. I was really hoping to use this as my project diary, so I'll try to catch up... for myself if nothing else. Part of the problem is that this site is so damn resourceful that for almost everything, I was able to find an answer to my pressing questions with the search function rather than posting on this or other threads. Good problem to have.

I got the engine running good enough to know I had a fighting chance. Last I posted about rebuilding the forks. They got a thorough clean, new seals, new spring guide and new oil. I buffed the aluminum and SS and they are looking good. With the forks off, it was an easy decision to remove the rest of the front end/handle bars. Each part I took off, I found more rust, dirt, gunk, etc. The more of that I found, the bigger this project grew. Pretty soon I made the commitment to just tear the whole thing apart. Clean, rebuild, or replace everything. As you know, there are several jumping off points...
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First the engine came off, along with the airbox, and bunch of other crap. At some point I decided to repaint the frame and for a while I was trying to remove as little as possible... nope.
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Simultaneously, I was working on restoring the gas tank. I have another project bike in line (CM200T), so I was working on that tank as well. Both were horribly rusted inside and I tried several things to get it in better shape before I did an Evaporust soak and then a POR15 full treatment. I was trying to do as many cheap treatments before the Evaporust in hopes that the Evaporust would survive and I could use it on other parts. I did a couple vinegar soaks. Several rounds of nuts and bolts shaking. I tried the electrolysis process mostly out of curiosity. All worked well, but only steps towards the final. The electrolysis was fun. I used an external hard drive power supply and a piece of iron rod about 3/8". With a tennis ball holding it in place I would leave it in there for about an hour, clean the rod and do it again. It seems like if I had continued this for a while, it might have cleared all the rust, but at some point I had to sleep. Next I did the evaporust which finished up the job nicely. I probably could have done the POR15 immediately afterwards, but I went ahead and did the 3 step process. Seemed to work well and both tanks have a nice inside coating. Discovered a pin hole as well that is now sealed. Bonus!
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