1972 CB175 K6

rapid_roy

rapid_roy

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Joined
Mar 22, 2021
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Location
New York City, USA
Hey all! I'm trying to get this ’72 CB175 in reliable, safe running condition.
I'm a motorcycle noob still, so thank you all in advance for sharing your wealth of knowledge and experience!

A bit of history. I bought this in Feb 2018 from the second owner, who had kept it garaged since the 80's. It did start when I bought it.

After that, it sat at my Dad's house for a few years. He had someone replace the rust-eaten mufflers, new clutch cable, new tires, and allegedly something with the brakes. Changed the spark plugs. The mechanic wasn’t familiar with vintage bikes (the mufflers they got blocked the kick start), so I’m not sure the work was well-done.

It was ridden a few times there by my dad. I picked it up in March 2021 and brought it to my house. The petcock had been left on, and it wouldn't start, so I took off the carbs and gave them a full cleaning, replaced float bowl gaskets.
Other work I did:
-new AGM battery
-changed oil with Shell Rotella T4
-cleaned gas tank rust with EvapoRust
-new petcock
-new kick start lever that clears mufflers (but I haven’t gotten it to start w kick)
-new fuel lines
-new gas cap gasket

I finally started it up in September 2021, and rode it around the block for 10-15 min. I think it stalled out when I came to a complete stop in 1st, and tried releasing the clutch. After doing that a few times, I couldn’t get it to start again. Maybe the battery was done?

Fast forward a year later, I moved again (Jersey City) and finally have time to get it working.

I got it to start a few weeks ago, and rode it around the neighborhood for about 15 minutes. I got it up to 3rd gear.

But problems arose when, again, coming to a stop and letting the clutch out in 1st gear. It kept stalling. It seems like the clutch lever was sticking, ie it wouldn’t release when I let go. The power was not engaging. It stalled about 4-5 times, and I couldn’t get it to start the last time.

Also, the gear shifter seems to get stuck. A lot of force is required to kick from 1st to neutral to second.

Last week I tried starting it again. Video below. I couldn’t get it to idle. I’m applying very little throttle, but the RPMs rev very high, then it dies.

https://youtube.com/shorts/eU7e3L8k8r4?feature=share
https://youtube.com/shorts/f46w29F_F-Y?feature=share

Someone told me I might have to take apart the clutch, and clean the clutch plates or get new ones. That should fix the clutch sticking/stalling issues. Since it was sitting for so long. But I’m not sure about the high RPM issues it’s having with starting now. What do y’all think? Thanks!
 
First, you should know that these carbs do not have accelerator pumps so twisting the throttle before cranking does nothing, you're only lifting the slides and letting them back down. Hondas typically like to start with very little throttle turned, close to idle position and if cold, using the choke in addition to keeping the throttle close to idle position. Second, it sounds like it's only running on one cylinder to me which would explain why it drops off and won't idle. Have you checked the plugs, and the points/timing as well?
 
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Before you tear into the clutch, try tying the clutch lever back to the bars and let it sit overnight, then give the kickstarter a couple of pokes with the lever still pulled in. When the clutch plates free up the kick lever won't turn the engine. Doesn't always work but it costs nothing to try.
 
mike in idaho said:
Before you tear into the clutch, try tying the clutch lever back to the bars and let it sit overnight, then give the kickstarter a couple of pokes with the lever still pulled in. When the clutch plates free up the kick lever won't turn the engine. Doesn't always work but it costs nothing to try.
Click to expand...

Thanks, Mike. That is a good thing to know to try.
 
ancientdad said:
First, you should know that these carbs do not have accelerator pumps so twisting the throttle before cranking does nothing, you're only lifting the slides and letting them back down. Hondas typically like to start with very little throttle turned, close to idle position and if cold, using the choke in addition to keeping the throttle close to idle position. Second, it sounds like it's only running on one cylinder to me which would explain why it drops off and won't idle. Have you checked the plugs, and the points/timing as well?
Click to expand...

Thanks Dad :) When I tried starting it, I had the choke closed, throttle turned in just a bit, as per the owners manual. I have not checked the plugs or points/timing, hoping I wouldn't have to go there. Should I go through the service manual and follow instructions? And buy a good compression gauge?

Mike, I actually did clamp the clutch lever down for a day before taking the video above, and trying to start it. But I didn't use the kick start, used the electric start. Does that make a difference?
Also I didn't get it to start, not sure if the clutch is still sticking, so it could have worked!
 
rapid_roy said:
Thanks Dad :) When I tried starting it, I had the choke closed, throttle turned in just a bit, as per the owners manual. I have not checked the plugs or points/timing, hoping I wouldn't have to go there. Should I go through the service manual and follow instructions? And buy a good compression gauge?

Mike, I actually did clamp the clutch lever down for a day before taking the video above, and trying to start it. But I didn't use the kick start, used the electric start. Does that make a difference?
Also I didn't get it to start, not sure if the clutch is still sticking, so it could have worked!
Click to expand...

Mike mentioned using the kickstart to check the clutch because the kickstart gear drives through the clutch, so if the plates are stuck the kickstarter will turn the engine over even with the clutch lever pulled. If you still have the clutch lever clamped to the grip, if you use the kickstarter enough it might break the clutch plates loose. And, if the engine hasn't been run in a while you should really go through all the tune-up items to be sure it has the best chance of running properly after sitting.
 
ancientdad said:
Mike mentioned using the kickstart to check the clutch because the kickstart gear drives through the clutch, so if the plates are stuck the kickstarter will turn the engine over even with the clutch lever pulled. If you still have the clutch lever clamped to the grip, if you use the kickstarter enough it might break the clutch plates loose. And, if the engine hasn't been run in a while you should really go through all the tune-up items to be sure it has the best chance of running properly after sitting.
Click to expand...

Thank you! I tried clamping the clutch lever for a day and used the kickstarter a few times. Once I get it riding, I'll see if the clutch is better. Also I can kickstart the bike to get it running now, which is good!

As you said, I think it's only running on one cylinder; I started it and tried babysitting it for a minute with the throttle turned a little bit. When I let go of the throttle around 1200 RPM, it died. I checked the engine, and the right muffler was much colder than the left muffler. So would that be fixed by the points and timing adjustment? I cleaned out the carbs recently, but then it was sitting for almost a year after that.

I adjusted the cam chain and valve clearances. I'm going to do the points and timing next.

One more question: I broke a spark plug and need a replacement. I see the manual says to use an NGK D-8HS plug. I looked online but I didn't see any obvious matches? The ones inside were NGK DR8HS, but I don't know if those are correct either. Could someone link a good one? Hoping to pick something up at Home Depot or Autozone today, but I realize I might have to special order.
 
DR8HS is the resistor version of the D8HS. You most likely already have resistor plug caps, so you don't want to use resistor plugs with them. If you can't find D8HS plugs you need to find non-resistor plugs caps
 
Thanks for the tip! I got new spark plugs, NGK 7112 D8HA. They work!

I checked and I’m getting spark from both plugs. Also checked both boots and wires and I’m getting spark there, but I think one of the boots is attached to the wire badly, does it look like it should be replaced eventually?

I adjusted the cam chain and valve clearances, and adjusted the points gap and ignition timing. I changed the oil and cleaned the carbs a year ago, I think that concludes all of the tune-up items that could be the issue?

Finally, I opened the carb float bowl covers to empty any gas while it was sitting. When I opened the ride-side carb, the main jet fell out! I guess it wasn’t screwed in tight enough and loosened with vibrations. So now both cylinders are firing when I run it; both pipes are hot and I can feel exhaust from the mufflers.

The bike starts easily now, but my issue is getting it to idle. The choke was closed when I started it (it was about 45 degrees F), I gave it a tiny amount of throttle. It was revving around 2kRPM, I was giving it as little throttle as possible. I tried opening the clutch, but the RPMs revved high, up to 5-6k.

After babysitting it for 2-3 minutes, I tried letting off the throttle in neutral, and the engine died. Same result when trying again.

Here’s a video of me starting it, sorry for the bad angle, I put the phone down to try shifting into 1st.
https://youtu.be/HiMQjevttxo

Does anyone know what could be wrong, or where to start troubleshooting?
 
The choke is only used to get the engine running when cold and should progressively be opened as the engine warms up a bit. Even at 45° you should be able to completely open the choke in about a minute, which explains why the engine sounds rough like it's "8 stroking" meaning only firing every other time it should because the fuel mixture is too rich due to the choke being on. Then, after running it as long as you did with the choke on, when you try to let it idle the plugs are overloaded with excess fuel so it stalls.
 
To me it sounds like a fuel starvation. It was fine upon starting but after the float bowls fell low the revs dropped. Check the petcock bowl and vent hole of the fuel tank filler cap.
 
Thanks for the detailed info AD :) I tried opening the choke a bit, but the RPMs went up to 5/6k, so I closed it again. Does that mean i should adjust my carb screws?

I'll try opening the choke after a minute tomorrow. Sorry, I'm new to motorcycles and don't know all the details of warming up a bike w carbs.
I really want to get this running! Starting to look at fuel injected bikes haha

Hondaholic, thanks. I'll loosen the fuel cap and check the vent hole. What should I look for on the petcock bowl?
 
rapid_roy said:
Thanks for the detailed info AD :) I tried opening the choke a bit, but the RPMs went up to 5/6k, so I closed it again. Does that mean i should adjust my carb screws?
Click to expand...


As mentioned, the choke is to enrich the mixture for cold starts and nothing else (and certainly not to control the idle). It's difficult to say why the rpms rise when the choke is off, but it's easy to say why the bike won't idle now, it's being literally choked to death. While I realize (at this point) that you're not familiar with carbs, all of this illustrates why everything needs to be addressed with respect to the engine's systems - valve/cam chain adjustments, points/timing, carb adjustments all work together for things to operate correctly. At this point we can't be sure why the idle is far too high so starting at the beginning is a requirement.
 
rapid_roy said:
. . . Hondaholic, thanks. I'll loosen the fuel cap and check the vent hole. What should I look for on the petcock bowl?
Click to expand...

Anything that shouldn't be in there, i.e. water (result of condensation) or remnants of rust or other particles from a previous tank clean or non-use.(y)

The few alternatives listed by others also should see your bike running spot on in no time!
 
The longer, narrower notches on my throttle slides (that rub the length of the whole slide) both face inward on my CB175. I have original Klein carbs. Looking inside the carb, there are notches inside that only allow one orientation of the slides. Unless I’m missing something? Would love to be wrong!
 
Again, the slides will fit either carb but they are oriented Left and Right - it's the cutaway on the back of the slide that matters. The cutaway should face the air cleaners

slide.png
 
ancientdad said:
Again, the slides will fit either carb but they are oriented Left and Right - it's the cutaway on the back of the slide that matters. The cutaway should face the air cleaners

View attachment 18779
Click to expand...

Thanks for clarifying that with the pic! Yes, the cutaways were facing back to the air cleaners.

View attachment 18785

Petcock bowl had a few specks in it but looks pretty good? I cleaned the tank recently and put a new petcock filter in.
 
The attached picture didn't take, nothing there. Glad the slides are correctly oriented, it's a simple thing that gets some people when they've had everything apart.
 
ancientdad said:
Again, the slides will fit either carb but they are oriented Left and Right - it's the cutaway on the back of the slide that matters. The cutaway should face the air cleaners
Click to expand...

That's today's lesson for me and when I venture into the garage next I will check mine are the right way round but just out of interest what are the symptoms of having them the wrong way round - presumably the idle screw will have no effect ?
 
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michaelgj said:
That's today's lesson for me and when I venture into the garage next I will check mine are the right way round but just out of interest what are the symptoms of having them the wrong way round - presumably the idle screw will have no effect ?
Click to expand...

Since the cutaway would be facing the engine, it probably wouldn't idle unless the screw idle speed adjustment was turned in all the way and still wouldn't idle right.
 
I've done this by accident (incompetence), and found that the engine revs immediately rose to 5-6k when the engine was started from cold, hasty grab for the ignition switch required !
 
Just coming in on this, but the video sounds to me like it is "one lunging" and trying to idle on one cylinder.....
Could be that loose plug boot connection, or carbs way out of sync....

Unscrew the cap from the wire, clip off 1/4" of the wire and re-thread the cap on/into it....

My Carb sync procedure is posted in the technical forum, in 66Sprint's Classroom....
 
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I have just checked mine and the idle adjustment notches are on the correct sides - how could I ever doubt my own abilities. I was aware the main "cutaway" needed to be facing the air filters otherwise the engine will race away when started but never gave a thought to these idle adjustment notches.

One less thing to worry about - now I can get back to restoring my wiring. The previous owner thought it would be a great idea to use the same coloured wiring (black) when he rebuilt the wiring harness, so I'm slowly replacing his botched effort with how Soichiro's team intended it - sorry not trying to hijack anyone's thread here. :sad:
 
Hey all! A lil update. After a winter in storage, I'm working on this bike again.

-both carbs/pistons are firing
-bike is idling at 1200rpm, I just adjusted the throttle stop screws -_-

The current issue is that it stalls when trying to shift from neutral to first. I think some clutch adjustment/cable lube is in order.

Hoping that solves the issue, and I don't have to rebuild the clutch.
 
Since it sat in storage for the winter, I suspect all that's "wrong" is the clutch plates are stuck. Hold the clutch in and kick the engine over with the kickstarter, it should break loose after a few kicks.
 
Thanks AD! I tried that. The whole cable/housing was replaced a few years ago, so I'm guessing it's not a lube issue.

I tried adjusting it for the right amount of freeplay. The clutch cable is very sticky. When I pull the lever in, it doesn't always release all the way on it's own. So it stalls out when trying to start in first.

I figured out that if I get the bike rolling with the clutch pulled in, I can shift into first pretty easily. Once I got it going, it rode it around the block a few times, and shifted into 4th no problem.

But when it's at a standstill, it just won't go! Sorry I'm not great at explaining. Anyway, I'll probably have to take the clutch apart and clean/lube everything, to get the clutch operating smoothly.
 
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