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1972 CB175: rebuild then restore

Next issue to fix is a bent center stand and missing spring. I also think the attachment point on the bike for the spring is missing
Would it be easier to fix the center stand or install a new side stand? I currently have the center stand tied up.1000000390.jpg1000000399.jpg1000000398.jpg
 
Center stand is working once again! I did not bend the stand back but the spring is now connected to the frame and it seems to function well enough.

I've also been working on a few other things with the bike. I set my timing and valve clearances, which seemed to go pretty smoothly. After setting the timing, my idle rpm went way down. It was reading around 800-900 rpm and needed to be given gas during a cold start to stay running.

I pulled the carbs and found that on the left carb the little spring pin under the float was not providing any spring to the float. I noticed previously that this carb periodically had some fuel coming out of the overflow tube. I'm guessing the two are connected and I might need to replace that component? Is there anything I can do to fix it or should it be replaced? I think that carb gets too much gas as a consequence. The spark plug is dirtier than the right, and I've had it backfire/ cut out before.

I've also read the carb adjustment instructions but remain confused about the steps. Do you adjust one carb at a time? If so, do you unplug one spark plug while you set each carb? If there are any trustworthy and good videos on the subject that could be shared with me, I would really appreciate them.
 
I'm really stuck with the carb tuning. I found that the default setting for the slide needle is to have the retaining clip on one of the middle slots. I noticed my slide needle was on the lowest slot so I switched it back to the default. The bike then seemed to run reasonably well, but it eventually choked out. I think the issue has something to do with flooding because once it chokes out, I have to wait a while to attempt to restart the motorcycle. I also noticed that my left spark plug gets sooty very quickly.

Could the float needle lacking any spring be the cause?
I'm guessing I'll need to purchase a carb rebuild kit to get another one. Is there a trick to refurbishing the old one so that it functions again?
 
I'm guessing I'll need to purchase a carb rebuild kit to get another one. Is there a trick to refurbishing the old one so that it functions again?
The most important thing to know at this point is that every carb kit for sale out there has inaccurate brass and other hard parts in them. Did you try loosening the spring-loaded pin in the float needle? It could just be stuck and with a little careful work with needle nose pliers and some penetrant it might loosen the stuck spring. If not, places like JetsRUs and Sirius Consolidated are good sources for accurate replacements.

 
The most important thing to know at this point is that every carb kit for sale out there has inaccurate brass and other hard parts in them. Did you try loosening the spring-loaded pin in the float needle? It could just be stuck and with a little careful work with needle nose pliers and some penetrant it might loosen the stuck spring. If not, places like JetsRUs and Sirius Consolidated are good sources for accurate replacements.

Thank you for the link! I just pulled the carb again and found another issue! It appears the float itself actually takes in fuel. I noticed as I pulled it out that it sound like some fluid was inside of it. The float needle seems to spring back when depressed slightly with a finger. Could the float having a little fluid in it be enough to depress the needle. I guess I'll need to replace the float.
 
Could the float having a little fluid in it be enough to depress the needle. I guess I'll need to replace the float.
The float needle may be okay, but the float itself allowing gas inside it definitely needs to be addressed. Sometimes you can re-solder the seams and stop the fuel leaking into it
 
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The float needle may be okay, but the float itself allowing gas inside it definitely needs to be addressed. Sometimes you can re-solder the seams and stop the fuel leaking into it
The float needle appears to work! I switched the good float to the other carburetor and it performed the spring action as it should. I think I've figured out the leaking side of the one bowl based on the sound. I tried submerging it in gasoline to find the leak but I didn't see any bubbles. I'm going to let the gas currently within the float evaporate and then I'll use a hand lense to try and locate the pinhole.
 
The float needle appears to work! I switched the good float to the other carburetor and it performed the spring action as it should. I think I've figured out the leaking side of the one bowl based on the sound. I tried submerging it in gasoline to find the leak but I didn't see any bubbles. I'm going to let the gas currently within the float evaporate and then I'll use a hand lense to try and locate the pinhole.
It's possible the leak is at a soldered seam on the float, the solder on these is old and can get brittle with age.
 
On further inspection, I found a small divot with a seam running out of it. After watching it a few moments, I could see gas slowly pooling at the area. I will wait for all the gas to evaporate and then try and solder it.
 
Ended up ordering a replacement float and installed it in the old carb. Measured the float height at 21mm and reinstalled both carbs. When I tried to start the bike up it began revving uncontrollably. I cut the bike off and the same thing happened. Read some older forums and found that it might have been the throttle cable linkage where the single cable splits into two. I adjusted that and it seemed to stop the uncontrollable revving, but now the bike wont start at all. Really not sure what to do now. I will post videos tomorrow.
 
Ended up ordering a replacement float and installed it in the old carb. Measured the float height at 21mm and reinstalled both carbs. When I tried to start the bike up it began revving uncontrollably. I cut the bike off and the same thing happened. Read some older forums and found that it might have been the throttle cable linkage where the single cable splits into two. I adjusted that and it seemed to stop the uncontrollable revving, but now the bike wont start at all. Really not sure what to do now. I will post videos tomorrow.

Well turns out I didn't stop the uncontrolled revving issue by shifting the throttle cable linkage. I started the bike this morning and it began uncontrollably revving once again. In order to start it, I had to have the choke on. Once it began running I took the choke off and the rpms went down a bit but not substantially. It was also backfiring a bit and it did not previously do that. Any ideas?
 
Well turns out I didn't stop the uncontrolled revving issue by shifting the throttle cable linkage. I started the bike this morning and it began uncontrollably revving once again. In order to start it, I had to have the choke on. Once it began running I took the choke off and the rpms went down a bit but not substantially. It was also backfiring a bit and it did not previously do that. Any ideas?
Pictures of the areas you worked on always help. Words rarely describe things well enough to make educated guesses in situations like this, because we can't see everything that was worked on or touched in a specific area where other things could have accidentally been affected as well.
 
Well turns out I didn't stop the uncontrolled revving issue by shifting the throttle cable linkage. I started the bike this morning and it began uncontrollably revving once again. In order to start it, I had to have the choke on. Once it began running I took the choke off and the rpms went down a bit but not substantially. It was also backfiring a bit and it did not previously do that. Any ideas?

make sure you put the slides in facing the right way when you reinstalled the carbs. the cutout should be facing the airbox.
 
It's worth taking the air filters off, so that you can look down inside the carbs, to see if both slides bottom out correctly when the throttle is opened and closed, also that they both lift simultaneously.

I've had issues with the 2-1 junction box on an aftermarket throttle cable, both with it sticking, also secondary cables not being quite long enough.
 
I think I figured it out! Revving issue is being caused by a bad throttle control that gets stuck and one of my slides was in backwards which was also probably contributing towards the issue. I'm probably going to take off the air filters once I get a new throttle cable. I'd like to get them sinked perfectly.
 
Uploading a video to see if you all think the bike sounds okay. It seems to run pretty good currently. This is a complete cold start. I also have the kickstart lever attached securely enough to the spindle that I can use it! Woohoo!

This link should take you to my a google album with the video: https://photos.app.goo.gl/NTDqQzXmJ2bcVy4G9
 
It's worth taking the air filters off, so that you can look down inside the carbs, to see if both slides bottom out correctly when the throttle is opened and closed, also that they both lift simultaneously.

I've had issues with the 2-1 junction box on an aftermarket throttle cable, both with it sticking, also secondary cables not being quite long enough.
This sounds like an excellent idea. Do you have any recommendations for aftermarket throttle cables?
 
make sure you put the slides in facing the right way when you reinstalled the carbs. the cutout should be facing the airbox.
I realized one was installed incorrectly. I thought I placed them in correctly but one must have slipped around when I was trying to wrangle the spring and throttle cable.
 
I'm currently planning for future upgrades/repairs and am seeking advice on a few things.

My battery seems to drain more frequently than I'd like it to. Would a regulator/rectifier upgrade help reduce the drainage or improve charging? I found on another vintage Honda twin forum this rectifier/regulator combo http://www.sparckmoto.com/Products/Detail/7. Is this my best option. I currently have a lead acid battery.

I also think my front and rear shocks probably need to be serviced. I was thinking of eventually replacing the rear shocks, but more importantly I would like to service my front shocks and replace any oil that may or may not be in there. Does anyone know of a good instructional video for this service? I will of course consult the manual, but it helps me to see the process as well.

Lastly, I think I have some oil leaking from in between my cylinder head/cylinder. I am hoping this is just a bad gasket that can be replaced sometime next winter. Is there any temporary repair I can do to correct the issue? Is this something that needs to be immediately repaired or can it wait as long as I monitor my oil levels?

Thanks in advance for any help!
 
I'm currently planning for future upgrades/repairs and am seeking advice on a few things.

My battery seems to drain more frequently than I'd like it to. Would a regulator/rectifier upgrade help reduce the drainage or improve charging? I found on another vintage Honda twin forum this rectifier/regulator combo http://www.sparckmoto.com/Products/Detail/7. Is this my best option. I currently have a lead acid battery.
Is the charging system all original at this point? Stock rectifier (#4) and separate regulator (#1) under the battery box, like the picture below?

honda-cb175k6-super-sport-1972-usa-battery-silicon-rectifier-magnetic-switch_bigma000159f23_343d.gif


If so, the Sparck Moto unit would be the best replacement for both of those, yes. While the original rectifier could be the cause of your battery drain, since you're using an old school flooded lead acid battery and they rarely last more than a couple years on average, the battery could be suspect as well.
I also think my front and rear shocks probably need to be serviced. I was thinking of eventually replacing the rear shocks, but more importantly I would like to service my front shocks and replace any oil that may or may not be in there. Does anyone know of a good instructional video for this service? I will of course consult the manual, but it helps me to see the process as well.
Rear shocks are replacement items, front forks can be rebuilt with new seals and fresh fluid. Not sure if there are any videos out there of it but probably, though you should always take any video with caution and a grain of salt as the people making them often only think they know the right way to do things. Using the FSM and asking questions here, accompanied by plenty of pictures of what you're working on, will be the best help you'll get.
Lastly, I think I have some oil leaking from in between my cylinder head/cylinder. I am hoping this is just a bad gasket that can be replaced sometime next winter. Is there any temporary repair I can do to correct the issue? Is this something that needs to be immediately repaired or can it wait as long as I monitor my oil levels?
There is no danger riding it as is until you can do the repair, and there is little to nothing you can do from the outside to slow the leak aside from re-torquing the head and that is unlikely to make a difference. You do understand that the engine will have to be removed from the frame to do the work, right? It's not a difficult job, just a lot of disassembly and reassembly.
 
Is the charging system all original at this point? Stock rectifier (#4) and separate regulator (#1) under the battery box, like the picture below?

honda-cb175k6-super-sport-1972-usa-battery-silicon-rectifier-magnetic-switch_bigma000159f23_343d.gif


If so, the Sparck Moto unit would be the best replacement for both of those, yes. While the original rectifier could be the cause of your battery drain, since you're using an old school flooded lead acid battery and they rarely last more than a couple years on average, the battery could be suspect as well.

Rear shocks are replacement items, front forks can be rebuilt with new seals and fresh fluid. Not sure if there are any videos out there of it but probably, though you should always take any video with caution and a grain of salt as the people making them often only think they know the right way to do things. Using the FSM and asking questions here, accompanied by plenty of pictures of what you're working on, will be the best help you'll get.

There is no danger riding it as is until you can do the repair, and there is little to nothing you can do from the outside to slow the leak aside from re-torquing the head and that is unlikely to make a difference. You do understand that the engine will have to be removed from the frame to do the work, right? It's not a difficult job, just a lot of disassembly and reassembly.
Thanks for the info! I didn't have time yesterday to check for the original rectifier and regulator. I'll try and have a look this afternoon and let you know what I find. Not really sure what to expect. i think the wiring harness was messed with by the PO so maybe they installed a new regulator/rectifier at some point.

As for the front forks, I will check out the FSM to get an idea of the process.

I'm aware of the gasket change being a bigger project. I know it might be a pain, but I think it is something that will have to be done, if I ever want the bike to stay clean. I think the oil leak has contributed a fair amount of grime to the frame and engine covers.

As always, thanks for the help!
 
Is the charging system all original at this point? Stock rectifier (#4) and separate regulator (#1) under the battery box, like the picture below?

honda-cb175k6-super-sport-1972-usa-battery-silicon-rectifier-magnetic-switch_bigma000159f23_343d.gif


If so, the Sparck Moto unit would be the best replacement for both of those, yes. While the original rectifier could be the cause of your battery drain, since you're using an old school flooded lead acid battery and they rarely last more than a couple years on average, the battery could be suspect as well.

Rear shocks are replacement items, front forks can be rebuilt with new seals and fresh fluid. Not sure if there are any videos out there of it but probably, though you should always take any video with caution and a grain of salt as the people making them often only think they know the right way to do things. Using the FSM and asking questions here, accompanied by plenty of pictures of what you're working on, will be the best help you'll get.

There is no danger riding it as is until you can do the repair, and there is little to nothing you can do from the outside to slow the leak aside from re-torquing the head and that is unlikely to make a difference. You do understand that the engine will have to be removed from the frame to do the work, right? It's not a difficult job, just a lot of disassembly and reassembly.

Finally got around to looking at the charging system. Based on my observation (photos attached) the charging system seems to be original. I'm guessing there is some different wiring that would need to be used for a regular/rectifier combo.
 
Next issue to fix is a bent center stand and missing spring. I also think the attachment point on the bike for the spring is missing
Would it be easier to fix the center stand or install a new side stand? I currently have the center stand tied up.View attachment 44997View attachment 44998View attachment 44999

How did you determine the proper spring length? I can’t get an OEM spring online, nor can I find out what the size it would be. I measured from the frame to stand attaching points both up and down. I just don’t know how much tension there should be when up (at rest). I measured 6 3/8 inch when up, and am guessing I need something around 6 inches; 5 or even 5 1/2 inches would maybe be too much tension.
 
And that's part of the mystery with his K0, I've found pictures online that have shown the spring with and without part #10 above. Here's the fiche for the K0, which doesn't show the spring attached to anything at the frame-connected end. And it's next to impossible to verify an attachment point on a black frame in pics that aren't completely clear.

honda-cl175-scrambler-1968-k0-usa-stand-step-cl175_bighu0020f6s0501_d5cb.gif
 
Here (pic) is what I believe is the attachment point on the frame for the K0, which is different than the CB and maybe other CLs as you note. the brake spring also attaches inward to that attach stem. I think the part is 50522-222-000, but it’s hard to find. Pic of that also.

IMG_20250523_104352192.jpegIMG_20250523_105642965.jpeg
 
To add, I messaged CMS to ask the length of 50522-222-000. I also asked for the length of 95014-72402, which I believe is 126mm (4.96 inches). They initially told me the former is the correct spring, but out of stock.
 
How did you determine the proper spring length? I can’t get an OEM spring online, nor can I find out what the size it would be. I measured from the frame to stand attaching points both up and down. I just don’t know how much tension there should be when up (at rest). I measured 6 3/8 inch when up, and am guessing I need something around 6 inches; 5 or even 5 1/2 inches would maybe be too much tension.
I wish I could help you out, but when I went to inspect and measure my spring for you, lo and behold, it was missing along with the little piece of metal used for mounting it to the frame. I'm not sure what size it was, but it seemed smaller than 5 inches.
 
Stuck again! Tried fixing my throttle cables and messed something else up. My throttle cable gets pulled when the bike forks turn right which causes the bike to rev uncontrollably. I thought I would try and fix the issue and replace the old cables all at once. I installed the new cable without removing any other wiring. At first I thought I was just having issues with the carb tuning because I was getting the bike to start but with a high idle speed. The bike then began not starting and I checked my spark plugs for spark. I determined there was no spark based on testing both spark plugs against the engine casing. I then found the fuse had blown. I replaced the fuse and had spark once again. Thinking I had solved the issue, I began trying to tune the carbs again. The bike started and idled for a while at high rpm. It then stopped and hasn't cranked back up. I noticed that the wire coming out of the points cover sparked against the points cover. That was then followed by a large pop. The pop sounded like a backfire but maybe even louder. It appears no power is making it's way to the spark plugs, the spark plug boots, or the spark plug wire. The points are receiving power. I attached a test light to the negative terminal on the battery and the test light probe to the points and it lights up when the points are closed. What should I be checking now. Lights, turn signals, neutral light, brake light, and horn all work.
 
Stuck again! Tried fixing my throttle cables and messed something else up. My throttle cable gets pulled when the bike forks turn right which causes the bike to rev uncontrollably. I thought I would try and fix the issue and replace the old cables all at once. I installed the new cable without removing any other wiring. At first I thought I was just having issues with the carb tuning because I was getting the bike to start but with a high idle speed. The bike then began not starting and I checked my spark plugs for spark. I determined there was no spark based on testing both spark plugs against the engine casing. I then found the fuse had blown. I replaced the fuse and had spark once again. Thinking I had solved the issue, I began trying to tune the carbs again. The bike started and idled for a while at high rpm. It then stopped and hasn't cranked back up. I noticed that the wire coming out of the points cover sparked against the points cover. That was then
followed by a large pop. The pop sounded like a backfire but maybe even louder. It appears no power is making it's way to the spark plugs, the spark plug boots, or the spark plug wire. The points are receiving power. I attached a test light to the negative terminal on the battery and the test light probe to the points and it lights up when the points are closed. What should I be checking now. Lights, turn signals, neutral light, brake light, and horn all work.
If there is something in particular I should take a photo of, I am happy to do so.
 
If there is something in particular I should take a photo of, I am happy to do so.
Everything in the areas of what you described in the previous post - points wiring with the cover off, throttle cable routing, etc. And when you said you didn't "remove any other wiring", were you talking about actual wiring or other cables? Generally speaking, replacing cables doesn't usually involve wiring except at the right handlebar switch. Terminology is important so we know what exactly you're trying to describe.
 
I have a little update with a few photos. Will get more photos tomorrow. I did not remove any wires in the process of adjusting the throttle cable. I only removed the the old throttle cable.

After posting, I removed the gas tank to get a few photos of the ignition coil and noticed a few things. As I was removing the gas tank, I bumped the black wiring on the ignition coil which caused the spark plug to spark. I mistakenly did not turn the key off from the ignition position, but I am glad I forgot to as it helped me realize the black wire coming out of the ignition coil might be part of the issue. I gently pulled on the black wire again and the spark plug once again showed some life. I plugged the spark plug back in and the bike began running and idling pretty well until it burned through the remaining fuel in the carbs.
PXL_20250603_204452038.jpg

As I inspected in ignition coil, I noticed this hot glue looking substance coming out of the top of the coil (photo below). Is this normal or does it indicate a bad coil? i think these might be the original coil. They say made in japan on one side.
PXL_20250603_204443715.jpg
PXL_20250603_204433631.jpg
Below is a photo of the wire coming out of the points. I initially noticed this wire spark at the beginning of all my issues. As you can see, it is definitely frayed and probably needing repair. Also, I've always found the rubber stopper on the wire strange. Where would this go? There is another rubber piece that fits nicely against the coil cover and the coil plate, but I don't see where this little bit of rubber should be placed.
PXL_20250603_201054809.jpg
 
That rubber grommet on the points wire fits into a recess on the cylinder head, holding the wire away from the hot metal.

This is my CB200 head, but essentially same as 175.
 

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That rubber grommet on the points wire fits into a recess on the cylinder head, holding the wire away from the hot metal.

This is my CB200 head, but essentially same as 175.

That makes a lot of sense! I will put it up there in the correct location. Thank you!
 
A

That makes a lot of sense! I will put it up there in the correct location. Thank you!
I was able to find the location for that rubber stopper, but there is no way the wire will reach there with its current length. I also inspected the attachment point between ignition condenser and the points and it appears the points wire is even more messed up than I previously knew (see photo). PXL_20250604_210325549.jpg
 
You might consider just getting a new wiring harness and redoing the whole bike. It's a tedious job but we're seeing and reading about a lot of deterioration issues. At some point it might be better to accept that this is more of a project than you hoped, and dig in.
 
You might consider just getting a new wiring harness and redoing the whole bike. It's a tedious job but we're seeing and reading about a lot of deterioration issues. At some point it might be better to accept that this is more of a project than you hoped, and dig in.

I think you are probably right. Just trying to delay the inevitable until the weather isn't as good for riding. I ordered a new wire for the points. I might try and fix the current wire until that one arrives.
 
Just make sure you have your cell phone with you when you ride, and a good strong lock with a chain so you can lock it to a tree or something similar!
 
personally I love stripping a bike down, complete dismantling, I do it with every new project I acquire, just to clean everything up and inspect/rebuild/repaint. its therapeutic to me.
 
Did a little experiment this morning with the ignition coil cable. I detached the old bullet connection and installed a new bullet connector. The bike started right up! Still having issues with my throttle cable and revving. Im going to take photos of the cable rout this afternoon. Hopefully once I get the route down, the revving issue will stop and I'll have a ridable bike again.
 
Installed new ignition coil and condenser yesterday. The bike now runs and idles well. Still working on getting it so the throttle cable is not impacted by the fuel tank. With the fuel tank off, I am able to turn the front forks side to side without any revving. Once I installed the tank however, it appears that the left throttle cable gets pinched by the fuel hose that runs underneath the bike frame. Will get some photos of the issue today.
 
Here are some photos. The second video on this google album shows the issue. If you focus on the throttle cable feeding the left carb, you can see that as I turn the handlebar the cable moves and then the engine begins revving. Turning seems to have no impact on the right carb even though the throttle cable and fuel line are positioned in the same manner. https://photos.app.goo.gl/NTDqQzXmJ2bcVy4G9
PXL_20250610_144554412.jpgPXL_20250610_144455421.jpg
 
The upper part of the throttle cable should be routed above the left front tank mount rubber, not below. That will add some slack to the upper part that is being pulled by the bars due to lack of enough length to accommodate the turn to the right (because the cable crosses over to the left side of the bike).

However, I'm not sure why you're running it with the choke on at least halfway, once it's running for a minute or so the choke should be off. And it sounds like it's only revving on one cylinder, possibly from over-richness.
 
The upper part of the throttle cable should be routed above the left front tank mount rubber, not below. That will add some slack to the upper part that is being pulled by the bars due to lack of enough length to accommodate the turn to the right (because the cable crosses over to the left side of the bike).

However, I'm not sure why you're running it with the choke on at least halfway, once it's running for a minute or so the choke should be off. And it sounds like it's only revving on one cylinder, possibly from over-richness
I rerouted the throttle cable as you suggested and that has fixed the revving issue. Seems to be running well now. I think I must have accidently bumped the choke lever or something. I typically don't need to use the choke.

Somehow in fixing the throttle issue I must have disconnected some electrical wiring that relates to the lights/blinkers. My horn, neutral switch, and electric start all seem to work correctly, but I no longer have lights or blinkers. I think the issue must be with wiring underneath the gas tank because I've checked all the other visible connections.
 
I think the issue must be with wiring underneath the gas tank because I've checked all the other visible connections.
Unless the main harness got pulled and it affected some connections inside the headlight case where all those relevant connections are from the right handlebar switch.
 
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