My CL175K7

These carbs are certainly 'edgy' to say the least.
Sad to think of putting the bikes away, but salt is on our roads already.
 
Some thoughts about 175 carbs, apologies for length.

I now have 5 pairs - two 653A CL175 carbs, two 306B CB175 carbs, and one pair of CB200 carbs.
Once removed from their respective manifolds it is very difficult to tell them apart, as the identifying code is stamped on
the mainfold, rather than on the carb body. I had always assumed that the actual carb bodies were all identical, and that by
swapping all the brassware around you could, for example, make a CL carb into a CB one, and vice versa. I am now not so certain.


My CB174 started life as a K4. I have since rebuilt it into a K6 frame and running gear. Before I laid hands on it, I don't
think it had been touched very much, which is an important point. Back in the day, these bikes ran perfectly when new, before
grubby little hands started pulling them apart. Fast forward 50 years, during which time who knows what parts will have been
swapped, floats adjusted, or just general wear, leading to the problems some of us experience !


After giving the CB175 carbs a good ultrasonic clean, and checking that the correct jets were present, needle in correct slot
and float levels correct, the bike ran as expected, while the K4 air filters were fitted. These are slightly smaller than the
later ones, with longer intake runners, no internal labyrinth in the air boxes, and larger air inlets. When I swapped these
for some CB200 filters, the bike refused to rev out, stumbling past 7k rpm. With the filters opened up by removing the
restrictions, performance was restored. Why this should be I have no idea, as I'm sure the actual K4 motor is the same as the
later ones. I suppose the carbs are matched to the air filters, although on paper the K6 carb spec is the same.


I got the CL175 before I got the CB175, and immediately tried to turn the CL into a CB175, changing the exhausts and carb jetting
to suit, as I thought. It would probably have been fine if I'd just cleaned the carbs and ran it as a CL. Instead, I fitted
aftermarket rebuild kits, gaskets and brassware, then wondered why it didn't run well. Along the way, I lost track of which
parts were original, and which carb they came from.


My CL now has ( I'm fairly certain ! ) CB175 306B carbs fitted, with the genuine Keihin 98 mains, 38 pilots, needle clip in
centre slot, running David Silvers pattern CB exhaust systems. Even so, it caught me out with its sensitivity to air filters.
Following the CB175 experience, I assumed that less restrictive filter was the way to go. In fact, it ran badly on these,
problem resolved by fitting unmodified (apart from foam) CB200 filters, which are same as K6/K7 filters, apart from a slightly
longer ( I think ) intake runner, to compensate for slightly shorter CB200 inlet manifolds.


Speaking of which, I haven't noticed any performance difference between the 175 and 200 manifolds. 200 manifolds have tappings
for vaccum gauges, which might be useful.


I can't see ( or with my limited abilities, measure ) any difference between 175 and 200 carb bodies. The CB200 only has 88 main
jets, mounted on different jet holders to the 175 items. CB200 jet holders have a few extra holes in the (?) emulsion tubes.
All else the same as the 175 carbs.


The CB175 and CB200 carbs have solid mixture screws, both my CL175 ones had a curious cross drilling near the tip. If the solid
screws are turned fully home with the engine ticking over, it stalls. The holed tips can be screwed in and the engine keeps
running, at least on my engine.
 
My mixture screws are cross drilled, the cross drilling is a large hole, about 1.5 mm dia.
one carb will stall the engine if the mix screw is down tight.
the same design of carb on the other side does not do the same!

Further, the mix screws seem to do nothing.
my tachometer says 1800 rpm that feels so close to stalling so maybe less, but still the screws do nothing.

I have found that the relation between the engine speed screw on the slide is very sensitive to the mixture screw, and if out of kilter, one side will run hotter than the other, the hot side running smokey rich.
I can change the heat by re balancing the speed and mix screws, and turn a smokey hot side to the opposite side.

atm I have a heat balance, but I am not at all confident it will be the same next time I start it.....

Is there a replacement carb available other than the pairs you can buy for a £100 or so?
 
911hillclimber said:
My mixture screws are cross drilled, the cross drilling is a large hole, about 1.5 mm dia.
one carb will stall the engine if the mix screw is down tight.
the same design of carb on the other side does not do the same!​.....The K3 on CB, CL and SL carb bodies ALL LOOK the same, but internally are not.....Additionally, While the taper is the same on K3, K4, K5 mixture screws, they are not cross drilled like the K6, K7 mixture screws, and CL bodies have smaller air jetting than CB or SL versions......

Further, the mix screws seem to do nothing.
my tachometer says 1800 rpm that feels so close to stalling so maybe less, but still the screws do nothing....As a general rule, mixture screws ONLY have significant effect BELOW 1350, maybe as high as 1400 RPM....... Correct idle speed is ~1300.....

I have found that the relation between the engine speed screw on the slide is very sensitive to the mixture screw, and if out of kilter, one side will run hotter than the other, the hot side running smokey rich.
I can change the heat by re balancing the speed and mix screws, and turn a smokey hot side to the opposite side.

atm I have a heat balance, but I am not at all confident it will be the same next time I start it.....

Is there a replacement carb available other than the pairs you can buy for a £100 or so?
Click to expand...

See Blue above
 
Richard Pitman said:
Some thoughts about 175 carbs, apologies for length.

I now have 5 pairs - two 653A CL175 carbs, two 306B CB175 carbs, and one pair of CB200 carbs.
Once removed from their respective manifolds it is very difficult to tell them apart, as the identifying code is stamped on
the mainfold, rather than on the carb body. I had always assumed that the actual carb bodies were all identical, and that by
swapping all the brassware around you could, for example, make a CL carb into a CB one, and vice versa. I am now not so certain.


My CB174 started life as a K4. I have since rebuilt it into a K6 frame and running gear. Before I laid hands on it, I don't
think it had been touched very much, which is an important point. Back in the day, these bikes ran perfectly when new, before
grubby little hands started pulling them apart. Fast forward 50 years, during which time who knows what parts will have been
swapped, floats adjusted, or just general wear, leading to the problems some of us experience !


After giving the CB175 carbs a good ultrasonic clean, and checking that the correct jets were present, needle in correct slot
and float levels correct, the bike ran as expected, while the K4 air filters were fitted. These are slightly smaller than the
later ones, with longer intake runners, no internal labyrinth in the air boxes, and larger air inlets. When I swapped these
for some CB200 filters, the bike refused to rev out, stumbling past 7k rpm. With the filters opened up by removing the
restrictions, performance was restored. Why this should be I have no idea, as I'm sure the actual K4 motor is the same as the
later ones. I suppose the carbs are matched to the air filters, although on paper the K6 carb spec is the same.


I got the CL175 before I got the CB175, and immediately tried to turn the CL into a CB175, changing the exhausts and carb jetting
to suit, as I thought. It would probably have been fine if I'd just cleaned the carbs and ran it as a CL. Instead, I fitted
aftermarket rebuild kits, gaskets and brassware, then wondered why it didn't run well. Along the way, I lost track of which
parts were original, and which carb they came from.


My CL now has ( I'm fairly certain ! ) CB175 306B carbs fitted, with the genuine Keihin 98 mains, 38 pilots, needle clip in
centre slot, running David Silvers pattern CB exhaust systems. Even so, it caught me out with its sensitivity to air filters.
Following the CB175 experience, I assumed that less restrictive filter was the way to go. In fact, it ran badly on these,
problem resolved by fitting unmodified (apart from foam) CB200 filters, which are same as K6/K7 filters, apart from a slightly
longer ( I think ) intake runner, to compensate for slightly shorter CB200 inlet manifolds.


Speaking of which, I haven't noticed any performance difference between the 175 and 200 manifolds. 200 manifolds have tappings
for vaccum gauges, which might be useful.


I can't see ( or with my limited abilities, measure ) any difference between 175 and 200 carb bodies. The CB200 only has 88 main
jets, mounted on different jet holders to the 175 items. CB200 jet holders have a few extra holes in the (?) emulsion tubes.
All else the same as the 175 carbs.


The CB175 and CB200 carbs have solid mixture screws, both my CL175 ones had a curious cross drilling near the tip. If the solid
screws are turned fully home with the engine ticking over, it stalls. The holed tips can be screwed in and the engine keeps
running, at least on my engine.
Click to expand...

Not going to argue further, but CB200 carbs (at least here in the US) are bored as 18mm equivalent venturi carbs while CB 175 carbs are 20mm (Both have 20MM on the top cap castings and 18mm slides)
 
Richard Pitman said:
Some thoughts about 175 carbs, apologies for length.

I now have 5 pairs - two 653A CL175 carbs, two 306B CB175 carbs, and one pair of CB200 carbs.
Once removed from their respective manifolds it is very difficult to tell them apart, as the identifying code is stamped on
the mainfold, rather than on the carb body. I had always assumed that the actual carb bodies were all identical, and that by
swapping all the brassware around you could, for example, make a CL carb into a CB one, and vice versa. I am now not so certain.
.
Click to expand...

My assumptions as well. My 2 pairs of 175 carbs are hopelessly mixed up as far as which floats, manifolds, and brass go with which bodies. If there are differences, it’s no wonder I’m struggling. Add to that my current 175 came without air boxes. I bought an eBay pair, but I have no idea which version I have (cb200, early or late 175 etc.), I assumed those were the same as well.
 
Thank you Sprint, interesting.
My cb is a K6 (1972) so different to Richards. It came with empty air boxes, so I fashioned filters from carb filter foam I used on my previous 1976 CB175 though most of my trials have been filter less. Adding the filters has not changed a thing.

As to tick-over, the engine will not drop further than 1800 shown on the tacho, it will simply cut out (mix screws @ 1.25 turns out, both sides) hence me questioning the accuracy of the tacho (in my bike rather than in general). Tacho shows Zero with engine stopped, so it's not hung-up at low speeds, new cable fitted from the start.
I guess if the engine is running 'ok' then that might be the best scenario for me. I have not had the bike on the road, so no idea about high speed running.

Sorry to Richard for thread creep, won't add my probs to his thread.
 
Well, about 1800 is the lowest running speed for carbs that have the slides transposed...... Are the slide cut-aways facing rearward?
Just because they fit the guides and align throttle stop ramp to screw does not mean they are correct......

(I know it's a dumb question and I probably asked previously, but symptoms are symptoms and it is an easy mistake to make)
 
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I admit I have assumes ,) the carbs were correct when I got the bik.
the crescent shaped cut away is facing the filter and of course are fitted to fit the speed adjustment screw so if thecut away faces the filter, they are correct, but Iwill check again!
 
I took the covers off the CL175 the other day, and refitted the chain guard which I'd repainted. Pumped up the tyres to the correct pressures, using new German bicycle track pump, which works well. Unlike the new genuine Goodyear dial type pressure gauge, which is going back to Amazon. Thought I'd bought a quality item, but it won't hold a pressure reading, so useless.

This afternoon I removed the carbs and fitted the Wincycles carbs. No time to test today, hopefully refit a battery at the weekend and see if works !
 
Hope you will!
my carbs are expected soon, need you to do the 'training module' for me...
Salts off the roads by now I recon.
 


Battery fitted, fuel on. Brief overflow from right side carb, soon stopped.

Full choke and it fired up almost straight away. Needed a bit of adjustment of the idle stop screws, mixture screws left alone, already set at 1 1/4 turns out. Once warmed up, and trapped throttle cable freed off, it idles reliably at 12-1400 rpm, responds to the throttle. I haven't risked a test ride yet, don't want to breach the Covid rules too much. May go out later in the week, after the Sunday bikers have finished drawing attention to our hobby. Quick video clip of bike running.

0GgoEVm.jpg


wincycles - YouTube
 
Just like that!
Wonder if mine will be the same...
They are in Birmingham now, so with me next week I hope.
 
Test ride this afternoon. Literally started badly, took a while to get it started and running on both cylinders.

However, once I'd got it going and out on the road it was fine. Running easily to the red line in first 3 gears. Went to Tesco to fill with fresh Momentum E5 fuel. Once hot, it refused to idle, engine cuts out on closed throttle, cured by screwing the throttle stops in a trace. Maybe I need to fiddle with the mixture screws.

I think the initial poor start today was simply that the plugs were fouled after sitting idling for sometime after starting it the first time the other day.

On the way back today it was pulling an indicated 9k rpm and 70 mph in 5th. I'm running a CB200 chain and sprocket set, but with the 175 (lower than 200) top gear.

Plug colours look OK. Lighter in real life than on camera.
 

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Good to read Richard.
Those plugs look like mine do currently after a long time on tick-over.
My Ningbo, China carbs arrived late yesterday and look really nice, really well finished. Hope to fit and try on Thursday.
 
ancientdad said:
So overall a success? Seems so.
Click to expand...

Yes, definitely. I was concerned that it wouldn't run properly out on the road, when in fact it now runs better than expected, carbs fitted straight out of the box.

No markings to indicate main jet size, carb needles only have three slots, clip in middle one, same carb sold as fitting CB, CL and SL 175's, when we know that original carbs had different settings for the three variants.

Just had another quick static running test, and found that it idled better with the mixture screws 2 1/2 ( two and one half!) turns out. And screwing them right in stops the engine running, so they clearly do have some effect !
 
Just back in from a 40 mile around the back roads by Bredon Hill. Supposed to be under lockdown, but the number of folks out and about, in groups, is unbelievable.

Anyway, bike is performing well, easily holds 60 cruising speed, and on the way home did an indicated 70 in 4th, uphill !

It does seem rather cold blooded, needs full choke to start, then choke kept on as it warms up. Also, it's a bit hesitant until it comes onto full throttle and 5k rpm upwards. After that, engine comes 'on song' and screams up to the redline. Plugs are now a lovely light tan colour, just like I remember my first 175 used to be.

So, I reckon it's a tad lean. OK on main jet and full throttle, needs richening lower down. Maybe raise the needles and/or fiddle with the mixture screws.

These bikes are never 'finished' …….
 
Richard, you've got a great bunch of 175s! They look amazing, you did a great job on restoring them.

Thanks for all the updates on the carb saga! What a pain. I just started taking apart the carbs on my CB175, and now I think I should just get the Wincycles replacements... cheaper than an ultrasonic cleaner!
 
I have a proper ultrasonic cleaner, and in my view they are over rated. Don't put dirty old parts in expecting them to come out looking brand new. Yes, they do get dirt off / out, but they don't work miracles.
 
Richard Pitman said:
I have a proper ultrasonic cleaner, and in my view they are over rated. Don't put dirty old parts in expecting them to come out looking brand new. Yes, they do get dirt off / out, but they don't work miracles.
Click to expand...

Thanks Richard, good to know! I'm glad I didn't impulse-buy an ultrasonic. As Jim suggested in another thread, I'm gonna try cleaning them in Pine Sol, then hot water, carb cleaner spray, air, WD-40. I've got plenty of parts I'll need to buy, so I'd rather just clean the carbs if possible!
 
Last edited:
I don't think most people understand what an ultrasonic cleaner is used for. It's not a miracle refurbishing, refinishing, make like new tool. It clean deposits off of metals. If the piece goes in with corrosion it'll come out with slightly less corrosion but a mostly unnoticeable difference. It does remove deposits from the jets nicely and cleans the passages as well. Use of a proper cleaning solution is also needed, I use LPS Precision Clean.
 
Back to the Wincycles carbs. I've done a few more miles on it, and the idle is nice and stable, wide open throttle performance is excellent.

However, it takes several minutes for the engine to run without choke on a cold start, even in the warmer weather of the last couple of days, and even then there is some hesistancy coming onto part throttle. My single walled DS header pipes are taking on a straw colour and my plugs are now a very light tan. So I think its running too lean for its own good.

So, I've just been down to the garage and swapped the unknown size Chinese pilot and mains for Kiehin 38 pilots and 98 main jets, using the Chinese emulsion tube / jet holders. Mixture and idle screws not adjusted from their current positions, Chinese needle left in middle slot as before.

After a battle with the float chamber gasket on one side, I got it leak free and started the engine. Perfect - I was able to take off the choke almost straight away and it settled down to a stable cold idle at just over 1000 rpm. Instant response to the throttle, hesitancy gone. Haven't been able to road test it yet, fingers crossed that I haven't messed up the full throttle performance.

I'm so pleased I've ordered a second set, from the link Graham posted.

Chinese jets on the left. I retained the jet holder from the Chinese carbs.

9KaGRsI.jpg
 
It's almost as if they didn't actually have samples of the carbs to copy, like they went from pictures or something even less accurate
 
Can you order just the jets for the Chinese carb? If so then I would suggest enlarging the holes on the idle/slow jet 1 drill size larger than they are to begin with.
 
Doesn't seem likely that they supply the jets separately, but if it works OK with the Keihin jets taken from my original carbs I'll be more than happy. Road test coming soon !

For that matter, it might be possible to buy new genuine Keihin parts ?

The Chinese seem to have made a pretty good job of copying the actual ( right hand side ) carb body.

EDIT

Just been for a ride. It runs well once warm, but it still takes ages to warm up, even with the ( apparently) larger pilot jets. Plug colour good with the 98 mains. Minor niggles really, still running better than on original carbs, several sets of those tried.
 
Most interesting...

Started the CB yesterday after a few days 'rest' to see what happens, long adjuster in hand, so full of confidence!

Tricky to start and run well on full choke, and takes a long time to warm up so it will tick over on its own, maybe 3 mins?
After 5 it ticks over at 1500 and I've left it there, throttle response is really good, exhausts even temperature. Hot start instant on elec start (haven't tried the kick start ever).

This will seem trivial, but actually popped it into 1st gear and RODE the thing up and down the cul de sac outside the house (for the USA, a cul de sac is the end of a dead end road in the UK), it is SO SMOOTH in first, goes well and the new brake linings need bedding in...Felt really nice, no helmet or anything so well worth it while the wife was out shopping.

Surprised how expensive classic bike insurance is in the UK, lowest quote is £63, worst is £108 ($80 to 120$ ish).
 
911hillclimber said:
Most interesting...

Started the CB yesterday after a few days 'rest' to see what happens, long adjuster in hand, so full of confidence!

Tricky to start and run well on full choke, and takes a long time to warm up so it will tick over on its own, maybe 3 mins?
After 5 it ticks over at 1500 and I've left it there, throttle response is really good, exhausts even temperature. Hot start instant on elec start (haven't tried the kick start ever).

This will seem trivial, but actually popped it into 1st gear and RODE the thing up and down the cul de sac outside the house (for the USA, a cul de sac is the end of a dead end road in the UK), it is SO SMOOTH in first, goes well and the new brake linings need bedding in...Felt really nice, no helmet or anything so well worth it while the wife was out shopping.

Surprised how expensive classic bike insurance is in the UK, lowest quote is £63, worst is £108 ($80 to 120$ ish).
Click to expand...

Except for the insurance costs (always aggravating), all sounds well. Glad it rides nicely, makes all that trouble worth it in the end. BTW, 5 years ago I lived in a cul de sac at the end of the development street we lived on, and there's one at the end of our current street as well (even in a neighborhood where all the lots are 1 acre each) :) it's a common term here as well
 
Pleased to hear that it works, and that you have taken the plunge !

Those insurance quotes seem reasonable to me, assuming that's fully comp. And of course, you'll have no no claims discount, regardless of how many years you have on existing car policies. From memory, I'm paying £130 on a multibike policy with Carole Nash, fully comp but each bike only valued at £2K each, and restricted mileage, 5K each, again from memory, maximum no claims discount.

Cul de sac - literally translates as Dead End !
 
Yes, seems those quotes are about right.
Comp, no NCB etc but bike value state as £6K (not agreed value), 1000 miles/year.
RAC was cheapest @ £65, so will go with them.

As an aside, following your comments on the new carbs, started mine again from cold this morning. Bit iffy on full choke, but started and caught after the 2nd electric stab and held on choke by twist grip for a min, 1/2 choke for another minutes and relax.
Both sides warmed the same, head end of DS down pipes going straw colour too.

Wheeled it outside onto the drive and left it ticking over and simply purring. Walked away for a few secs and heard a CRASH as the bike fell over off the side stand...
Underestimated the slope of the drive for drainage which 'almost' negated the tilt angle of the bike so it must have been almost totally balanced when I left it.

Broke the front brake handlebar lever and nothing else marked! Lucky or what?
Missed hitting my old Porsche by a few mm.

New lever on it's way from WEMOTO

I suppose that's christened it now.
 
Wow... good for you that nothing more happened. As you say, the christening is over now most likely. That'll teach you to walk away and leave it unattended!
 
Back in the day, I came home one day and parked my CB175 side on, on the side stand, behind my Dads Morris Marina ( don't laugh please ), bike leaning away from the car.

So when my Dad reversed his car without checking behind him, my bike was pushed onto the side stand, which dug in, bent the stand and its mounting bracket, before the bike crashed to the floor.

Neither of us was very pleased, 'silly place to park your bike' etc, but he did buy me a new stand. It was never the same, as the bracket was still bent.
 
Just checked the needle position on the Wincycles carbs, clips were in the top notch ( of three ), leanest position. I've now moved them to the middle position, see if that helps the hesitancy coming off idle up to around 5k rpm.

I could have sworn clips were in middle position when I first looked at the carbs, another Spec Savers moment I suppose....
 
Brief test ride, raising the needles a notch seems to have sorted the fueling, pleased with how it's running now. Must have covered a couple of 100 miles on these Wincycles carbs now, better than I thought they'd be.

In summary, needles in middle notch ( of three ), Chinese unmarked jets swapped for Keihin 38 pilots and 98 mains. Bike running DS Silver pattern CB175 pipes, CB200 air filters with RamAir foam, Charlies ignition.
 
Amazing that there are aftermarket carbs out there that actually work well for a decent price. So much fiddling with the older carbs makes this solution very welcome, I'm sure.
 
Just back from yesterdays ride. Note the colour of the header pipes, and yes, I did remember to turn the fuel off before I put it away.

FyXM4He.jpg
 
That sounds very clean running Richard.
Wonder why your petrol tap is on the opposite side to mine?

My new tap came from DS and I found the OFF position was with the finger of the tap turn running 12 to 6 o'clock, fuel ON is at 9 o'clock.
 
My CB175 fuel tap is exactly the same as yours, but the CL175 tap is on the other side, so the tap lever positions are visually reversed but actually the same, if you see what I mean.

To avoid confusion, I actually printed a photo taken from the owners handbook and left it in the garage as an aide memoir.

CL tap differs in that instead a flat flange fitting as the CB, it screws onto a threaded spigot on the tank.

TpMXqvN.jpg

Hy9igH8.jpg
 
Interesting, as in that position fuel flows down the tube,(only checked one tube) but with the lever @ 6 o'clock it stops flowing....
Typical for this bike!
 
Nothing to report buildwise, but yesterday afternoon I had a break from hedge trimming and backyard carpentry, and took both the 175s out for a spin. Not at the same time, obviously.

They seem to enjoy this hot weather, both started easily after standing for best part of a month, and behaved themselves with nice idle both hot and cold. Each one got an hour each of sound thrashing around the local roads. Very satisfying when after being passed by morons in BMWs to pass them in turn as they fume sat in traffic. What is it with drivers of German cars ? ( Porsche excepted ).
 
Richard Pitman said:
Very satisfying when after being passed by morons in BMWs to pass them in turn as they fume sat in traffic. What is it with drivers of German cars ? ( Porsche excepted ).
Click to expand...

Over here, you can't even make the distinction between German brands. BMW, Mercedes/AMG (all money gone), Audi, Porsche and sometimes even higher-end VW drivers are all jerks (at least in my area) along with the other high-end brands too like Cadillac (Escalades in particular), Hummer H2 and the more rare sighting of a Ferrari, Lamborghini, Alfa Romeo or even a Bentley... they all "think who the hell they are" so to speak.
 
Sweet! Looking forward to my saga soon. Hopefully it will go smoother for me. Maybe a little or (lot) fumbling makes the final riding experience more enjoyable.
 
Went for a test ride this morning, bad misfire over 6k rpm, wouldn't rev out cleanly to the red line. This is on the motor that I've just refitted, but was in good running order previously.

Quick pit stop for a plug swap, improved matters quite bit, but still not right. Carbs haven't altered, were working fine on engine that's just been swapped out, so I think issue has to be ignition related. I swapped my Charlies Place ignition over from the outgoing motor, and did scratch my head a bit over getting it timed correctly, but thought I'd got it right eventually.

Does the polarity of the ignition coil LT circuit matter ie which wire +12v is connected to ? ( After market coil with orange and white leads, assume orange is +ve )

All else fails I'll try fitting a contact breaker set up.
 
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