Rebuild of my English CB175K6, 1972

Thanks all, you have summed-up how I feel.

Some way to go tomorrow I hope to fine tuning the bike, but it does sound good, crisp and all that, and if the tick over is still 'above' the tuning of the primary mixture adjustment I don't care!
I simply want it to reliably start and run.

The big red battery I'm using to do all this repeated starting is coping well, it is a mighty battery, the new one in the bike is far less, so it must start readily.

The cylinder head cover gasket leak is a pain.
Porsche engines have a similar issue, and under the cover head bolts they use aluminium washers that crush and seal, but they are not subjected to the rigors of cylinder head nuts, but the design (M8 nuts) does work.

You can buy steel washers with integral seals, can remember the name of them now, but that is an alternative.

Anyone else had this leak problem and found a good fix please? I have stainless thick form washers under the dome nuts at the moment.
 
It's such a relief to hear the good news after all the trouble you ran into. It's great motivation to keep on tinkering away, even when things aren't working right.

Congrats!
 
Yes, progress at long last.

Those seals are called Dowty Seals here in England. They have a rubber lip in the inside diameter of the washer but a hard steel washer fae.
 
I've never had the stud nut washers leak when using the correct washers and acorns......
I'm guessing the SS ones you are using cannot deform enough to provide a good seal.....
Not leaking is prettier than shiny hardware.........
 
Thank goodness for that !

Any idea what the final diagnosis was ? Just not cranking over quickly enough on the starter ?

I've sometimes got similar starting issues, if they don't catch and run straight away, I think battery condition has a lot to do with it. Usually end up taking the plugs out and swapping them for new / dry ones, then it starts.

Never had a leak from that nut. I'm using the original Honda washers and stainless acorn nuts.
 
Always good to read your 'real-life' experiences Richard, hope you keep following this drama!
Can't help do this post:

Wheeled the bike and it's table outside, too many complaints from The Boss about carbon monoxide fumes in the adjoining kitchen...

More fuel, a good close check on the movement of the slides on each side being equal, need some more help on that below.

Choke on. Buzz the starter on the Big Battery and Vroooom off it fired within 3 seconds. Ran at 3K as I progressively eased the choke off and felt for exhaust temperatures.

Blow me if they both warmed the same! NEVER done that before.

Ran it till nice and hot (about 2 to 3 mins) measured by the silencers by the rear pegs being just about untouchable , though I am a wuss when it comes to hot things!

Now to the finer things in Honda Tuning.

Tried to ease the tick over down to a reliable put-put-put, 1/8 turn on each carb at a time, exhausts still even temperature, but the occasional spit from the carbs, random, no rhythmic timing to the sound. ( no filters on).
Will hold, just, about 1500 rpm on the tach but will abruptly die after 1 minute. Restarts instantly.

It does not sound clean and crisp, revs really well, dies to tick over like a car does. Maybe I'm expecting too much refinement?

Charging the small bike battery now, filters on while that is going on, then try tweaking again.

So, just why has this bike changed as Richard asks?
As ever, I changed a lot of things at the same time (sorry Sprint).
Cam timing 360 different to what I had before. I think I must, by accident ,have done this on my gold cb. Crate of beer owed to Sprint.
New Starter clutch (from DK) so I can give the engine a continuous crank backed up by the big battery cranking but still delivering 12+ volts to everything else. No more nasty starter noise.
New coil pack (same condenser though) Gives a fat spark both sides.
Endless checking of the timing. I am now good at splitting the difference.
Huge fuel supply by opening up the bottom of the reservoir and making a T piece with 5mm dia holes. Fuel flow at least 10 times stronger.
Some good well chosen swear words learnt and rehearsed over 50 years of tinkering...

As an aside, I found during all this the generator wires had popped out of their plastic housings, only the green Neutral wire was sound. I've fixed this now, male and female connector barbs sprung out to give a solid registration in the plastic.

however, all the generator wires are the same colour! Even under the thermal protective braided sleeves the wires coming out are a creamy white, but the manual shows colour to colur on the connector I've fixed, so not sure just how critical it is to get the right colour to colour as one side (3 wires) are all the same!
Any advice please?
 
911hillclimber said:
Blow me if they both warmed the same!
Click to expand...

While I realize expressions vary in meaning in different parts of the English speaking world, consider that this means something sexual in the US...

911hillclimber said:
Any advice please?
Click to expand...

Unless you've cut the wires (or the PO did), the colors don't matter as long as the plugs are intact but yes, there should be a pink, yellow and white IIRC
 
Those wires tend to fade and turn the same color over time. There are measurements that can be taken to decipher which is which. I’m sure Steve will chime in with those numbers.
 
I think the English expression 'Blow me down' was in common ( and completely innocent ) usage well before it was misused by you lot !??????

Can't even use an affectionate name for a cat anymore, since your last President went around grabbing them. On the other hand, you use the word 'fanny' to mean backside, over here it's much ruder.

What Does "Blow Me down" Mean? (with pictures) (wisegeek.com)

And we still haven't forgiven Dick Van **** for his performance in 'Mary Poppins'.
 
Richard Pitman said:
I think the English expression 'Blow me down' was in common ( and completely innocent ) usage well before it was misused by you lot !������

Can't even use an affectionate name for a cat anymore, since your last President went around grabbing them. On the other hand, you use the word 'fanny' to mean backside, over here it's much ruder.

What Does "Blow Me down" Mean? (with pictures) (wisegeek.com)

And we still haven't forgiven Dick Van **** for his performance in 'Mary Poppins'.
Click to expand...

All well said Richard, never meant that it was at all one-sided. We here are possibly the most vulgar-referencing country on earth at this point, some of the latitude in "news" headlines is hideous and likely has my parents and grandparents spinning in their afterlives. Had 911hillclimber added the word "down" to the phrase I wouldn't have paid any attention to it at all... oh, and I can't recall the last time I used the word fanny for any reason. That's actually a couple or three generations older expression here now. As for the Mary Poppins performance, I can't speak to it as I've never been interested enough to watch the movie
 
I shall look FAR more carefully at my English from now on!

As to the bike:

Fitted the filters, and the whole machine sounds better, more comfortable to the ear...
Even better, it has cold started 4 times now really easy and warms quickly and both sides are even in rate of heating and final heat so carefully tested by hand.

Got to the end of the general tidy up of the machine, rear chain on etc and while it was ticking over (1500 rpm indicated) opened the idle mix screws a 1/4 turn more, so both at 1/75 turns out from tight which made it sound better still.

Tried switching on the lights while it was running and immediately the engine stopped. This has never happened before, so i suspect that generator loom.

The only disturbance of the wiring is that generator/loom plug where I guessed the connections BUT, now I have printed my Sprint Lesson for the Day, that will be my task for tomorrow assuming I can get the connectors out!

Sprint (I don't know your name, sorry) I was not aware such wisdoms were on the site, better now I know.

Finally tonight I removed the plugs after the light switch had stopped the engine. Both black sooty and dry, but both the same, so running rich and one carb can sometimes flood/overflow so thinking of a full jet/needle/seat kit for the carbs.
Unnervingly, the Haynes Manual says the ignition could be suspect too! Not going there.

Sorted the leaking dome head cylinder nut. The nut was bottoming on the one stud before the washer was compressed tightly even though I checked the nuts before the lot was torqued, shows how much crush there is in the 3 gaskets.
Managed to get the stud down deeper and ran a plug tap down the nut and all is well.

"Goodness gracious me, getting to the end" might come to mind.;)

Wife thinks it sounds great and is now done.
 
Unless you can get genuine Keihin parts an aftermarket kit of jets and needles will just cause even more grief.

Even David Silvers float valve kits are aftermarket ones. In my limited experience, rich running can be sorted by attention to float level, float valve assembly, and height of carb needle, try dropping it one notch.

I'm tempted to try fitting the float valves from one of the (smaller choke) chinese carbs. Nylon floats and viton tip on float needle, just like in a modern Keihin carb.
 
Yes, I'm in the same mind frame.
I have the pair of the smaller ones as you know, just in their boxes now, but could be worth a try. A viton tipped needle would be better than the stock metal to metal.
Job for Saturday I think, wires tomorrow...
 
911hillclimber said:
Got to the end of the general tidy up of the machine, rear chain on etc and while it was ticking over (1500 rpm indicated) opened the idle mix screws a 1/4 turn more, so both at 1/75 turns out from tight which made it sound better still.
ANY "tickover" speed in excess of maybe 50 RPM above specified idle speed puts you partially on the main jetting, not just the idle jetting ......
Adjusting the mixture screws there is futile and may be leading you astray.......Try getting it down below 1250/1300 before tinkering with the mixture......

Tried switching on the lights while it was running and immediately the engine stopped. This has never happened before, so i suspect that generator loom. Alternator working or not (disconnected) should have ZERO effect on engine running if battery is good....Racers run "total-loss" all the time....

The only disturbance of the wiring is that generator/loom plug where I guessed the connections BUT, now I have printed my Sprint Lesson for the Day, that will be my task for tomorrow assuming I can get the connectors out!

Sprint (I don't know your name, sorry) ( Steve....And I don't know yours either...) I was not aware such wisdoms were on the site, better now I know.

Finally tonight I removed the plugs after the light switch had stopped the engine. Both black sooty and dry, but both the same, so running rich and one carb can sometimes flood/overflow so thinking of a full jet/needle/seat kit for the carbs.
Unnervingly, the Haynes Manual says the ignition could be suspect too! Not going there.

Sorted the leaking dome head cylinder nut. The nut was bottoming on the one stud before the washer was compressed tightly even though I checked the nuts before the lot was torqued, shows how much crush there is in the 3 gaskets.
Managed to get the stud down deeper and ran a plug tap down the nut and all is well.

"Goodness gracious me, getting to the end" might come to mind.;)

Wife thinks it sounds great and is now done.
Click to expand...
See above in Blue.....They are never "done".... Maintenance is a constant requirement......
 
Thank you Steve, the lights switching the engine off is strange, but I'll do the generator loom check anyway.
Are the Honda tachometers accurate as the engine sounds very slow compared to the needle position.

Just like my classic cars, never done as you say.
Graham.
 
911hillclimber said:
Thank you Steve, the lights switching the engine off is strange, but I'll do the generator loom check anyway.
Are the Honda tachometers accurate as the engine sounds very slow compared to the needle position.

Just like my classic cars, never done as you say.
Graham.
Click to expand...

Graham, The ONLY ways I can imagine that switching on the lights would Kill the engine would be :
A; Direct short to ground in the lighting circuit, but that would likely blow the fuse.....
B; White (lighting wire) and White with Yellow tag (alternator wire) are transposed inside the headlight shell.......
 
Thanks Steve, I'll have a look tomorrow or Saturday. Wife wants to get out of the house, flippin' Lockdown very tight here.
Everything was fine before the engine came out so only the generator/loom connector has been disturbed, but you never know...
It did it twice when I repeated the light switch on, so the fuse is ok.
Graham.
 
Battery terminal not quite tight can act similarly, add load and it causes loss of connection. And, since we're exploring other possibilities, corrosion in the ignition switch terminals can cause it too. The switch can be disassembled to clean the contacts inside on the back of the bakelite board the wires are soldered to.
 
Off topic, sorry.

Wife wants to get out of the house, flippin' Lockdown very tight here.
Click to expand...

Have you been called for your Covid jab yet ? Worcester is ahead of the curve, folks in the 65+ group getting done now. Wife and several friends have got theirs, still waiting for the call myself.
 
My money is on the switch too. The engine stops immediately I turn it to running/lights on (3rd? position) so, generator wires then the switch this morning.

As to the Covid Jab, not been called for Richard yet.
I'm 68 and wife 67, they have not got to us yet in the built-up areas. My mother is 100 in May, just had hers!
I expect end Feb, but could be before.

Really impressed how fast this vaccination has moved through the country, nearly as quickly as the Covid thing!
I recon 2/3rds of the population by Easter.
 
911hillclimber said:
My money is on the switch too. The engine stops immediately I turn it to running/lights on (3rd? position) so, generator wires then the switch this morning.
Click to expand...

Do you mean that the bike is running and when you turn the ignition switch to the 3rd position, the engine shuts off? If that is what you're saying, then there may well be nothing wrong. The 3rd position of all of Hondas ignition switches since about '69 has just been "Park", taillight only. Engine does not run in that position, only the taillight for roadside breakdown situations. Only position 2 is full power to everything. Headlight/taillight for normal riding should be controlled by the right handlebar switch
 
UK CB175s have a separate light switch in the headlamp shell, three positions, OFF, Sidelight, Main and Dipped beam. Handlebar switch control is just Dip / Main beam. Much better than the lethal handlebar switch that goes OFF / DIP / MAIN, too easy to turn off the lights when dipping from main beam.

Ignition switch is the same US or UK, OFF / RUN /OFF with parking tail light.

Back off topic, just had the phone call for my jab next week. I'm nearly 67, wife is nearly 69.
 
I think the switch is Kaputt. Someone else has been in there...
The bike is UK, so Off
1st position, all works
2nd position kills engine, headlamp comes on as does tail light.

I admit I clean forgot about the headlamp switch so things may be ok, but the ign switch itself is broken where the 3 tabs locate in the (cracked) plastic sleeve.

Although I loose the 1 key for ign and seat, I prefer the reliability aspect.
 
Graham......

IF your "key" switch has only three possible positions, Fully anti-clockwise is OFF....
One "click" clockwise is the normal ON/RUN position, everything works/can work, but the lighting must be turned on by a different switch (apparently in the headlight shell according to Richard) with the dip/beam control on the handlebars...
The second "click" clockwise is the PARK position and ONLY the parking filaments in the headlight (UK model) and taillight receive power.....This position NORMALLY shuts down the rest of the bike.....On the US models, there is no associated filament in the headlight shell, and Park only lights the taillight run filament......

Richard....

There is NO "off" position between low and high beam on the US switching, rather during the change, both filaments are momentarily activated......
 
It was the head lamp coming on in the final position that threw me, the side light obviously is almost a glow rather than blinding.
As said, a new one is on its way for £14 delivered.
I used to be the Design Director for a very well known lock business here in the UK so might consider changing the tumblers, but the lock I have is riveted together and has inside a plastic disc and two detente balls and springs to index for the positions, bit too much messing, so will have a nice bright key for the ignition, and an original one for the iffy seat lock.

In the mean time I need to fix the flooding of the RHS carb.
Going to try to fit the Chinese float and Vito needle to the stock carb, I think the metal to metal of the original design is a bit flawed.
the lhs is fine.

Have sorted the generator loom pin out using Steve's guide.
Another cold start to do this and with choke on, instant start, warm and off choke a minute later and both side hot as each other.
You cannot know how GOOD it is to 'boast' this bike now does this repeatably. 5 times in a row!

The light in this tunnel is really bright atm.

 
I dismantled the seat lock to make the ignition key fit, very simple job.

Steve, my point about the US light switch is that if you are heavy handed / wearing thick gloves, it is possible to push the switch slider from Main beam, straight through Dip beam into the Off position.
 
Might give that a go Richard, but see later:

A few hours tinkering and snagging today with good effect, but maybe 1/2 a step back.
1
Carb flooding.
The rhs carb has persistently flooded at times so this was job #1 today.
Removed it and found some small cloth fiber strands in the needle/seat area, so flushed that out. While apart tried the plastic float and hooked viton tipped needle from the new Chinese carb to the stock carb and all fitted. Put fuel to the carb, and it flooded!
Back to the old parts and on stripping found a small piece of swarf now at the carb needle seat...must be from when I modified the petrol reservoir, so, cleaned that all again...
Replaced the stock parts and no flooding.
Back on the engine and fingers crossed.
2
Ignition key
Put it all back on so I could run the engine (to check the carb etc).
Bloody thing fully functions, even the headlamp/side etc all work.....Will still fit the new one when it arrives next week, and check the key with the seat tumblers.
3
Brake light stopped working I found during the above light test, so with meters checked all that, changed nothing and it works! Must have been the green wire from the switch (new) to the loom as I pulled it and re-instated.
Is this bike spooked?
4
Started the engine to check the carb. All's well, not a drop of fuel.

Made the mistake of tinkering with the carbs while it was running. Still grey smoke from both and after my diligent fine tuning, the LHS is a little cooler than the RHS.
Got the tick over to a reliable 1500 indicated, but it is not happy. Should be smoother I feel.
The LHS (7/8 of the RHS heat) tick over adjuster screw has no effect, it is screwed out and the piston is on the floor of the carb, outer cable 3 mm loose so not holding it off.
RHS is almost the same so there is nothing more mechanically to drop the tick over.

Still a lot of water drops from both silencer ends and also the engine cylinder vent tube. Condensation if you like.
5
Head stud that was weeping oil now doesn't, but the same one on the other side now does!
Is this bike spooked??

Going to leave it alone now until the ign switch arrives.





 
England has unfrozen around here, so safe to go out to the garage. Covid jabs taken and recovered from, minor issues for me, a bit harder for the wife, but Round 1 done, 2nd jab in early May.
Brilliant!

To this bike again.

Put the new switch in and managed to eradicate one set of connectors to the loom. Electrics are better with as few connectors as possible I recon.

All works, key even opens the seat 'lock' but so does a small flat bladed screwdriver...

The carbs are still an irritant and a barrier to finishing the bike off and getting it on the road.

Richard suggested dropping the needles one notch down to lean things out a tough, good idea but the needles are already at max depth!
Didn't expect that.

I'm not sure if weakening the mains will help with the high tick-over and reluctance to go to a lower tick over, I can't get it to hold below 1500 indicated.

The water content from the silencers and the engine vent tube:

Does this indicate rich running or not bad at all?

Any ideas what to do next?? I don't see any point to getting new Chinese carbs, now available in UK for about £70 the pair.
 
Water ( combustion product ) from the exhaust and vent tube is perfectly normal, in my experience. Should stop once the engine is fully warmed up up ie taken for a run, water is still there but emitted as invisible steam.

Whilst warming up, my Hornet emits loads of water from the exhaust. Not so much from the breather ( which in any case is routed into the air box ), but then this is a much 'tighter' engine, water cooled tolerances.
 
Thanks Richard, Fingers crossed it will all clean up in the Spring on the road.
as to mixtures...unless I change the jet sizes, not much to do?

Do you think a change to the Chinese carbs will do anything to help?
 
The Chinese carbs. When I get around to it, I'm going to fit these to my SL175 alike and see how they run. My two road legal 175s are both on Keihins and run reasonably well. The CB175 is the best one, starts and idles correctly, due mainly I think to being as close to original spec as possible, including the carbs that it came with, points ignition etc. The CL175 has had several different sets of carbs, along with a CB175 pattern exhaust system, Charlies ignition etc. Running reasonably well at the moment, doesn't idle as nicely as the CB, but fine flat out.

I have to confess to not having done anything to the bikes in the last 3 months. I'm sure I'll get motivated soon. My neighbour was in his lock up yesterday, running up one of his bikes, Spring is in the air !

Off topic and probably boring, I've been closeted in the back bedroom, playing with computers. Scan have done well out of me recently. I used to know this stuff, but times have moved on ….
 
Thanks for the reply Richard.

Glorious in the garage this morning, so had another go at the carbs.

Fuelled-up, ign on and it promptly flooded out of the RHS carb, just as it has done before!
Carb off etc, found nothing.
Back on, still flooded but tapped it with the handle of a screwdriver on the float bottom casing and it stopped.

Started quite well and ran.
LHS heat lagged behind the RHS but came even after about 2 mins.

The heat balance is linked directly to slide position on this bike, tick over just about continuous at 1600, LHS carb has tick over screw fully screwed in, RHS carb about 1 turn out.

As said above, needles are in the fully lean position, so going to raise then 2 grooves and see what happens.

I'm sure my gold bike eventually ran better than this one.
Tempted to buy the Chinese twin carbs you have (now on ebay direct and £70 delivered, and if anything, transfer the stock jets etc over to the new carbs (if they don't run correctly).

The engine just doesn't sound right.
 
Stripped the carbs back yet again and set the floats to 21mm off the gasket face, both carbs were 23mm.
Blew all the passages again, and set the needle clip to 3rd groove (of 5) instead of first/weakest/groove.

Bike ran awful, really lugging at best.
Reset the needles to weakest, ran much better (clue) and got at one point 1800 rpm, almost smooth, almost equal silencer heat (but not the same to the touch).

Pulled the plugs, really really black soot and took some cleaning.

In conclusion, the bike is running far too rich.

Going to transfer the jets etc from the Chinese carbs to the stock carbs and try that.
If that fails it is a pair of the Chinese 'cb175' carbs like Richard's or fresh jets etc from K/L (stated to be Japanese made for Honda).

Cost is about the same.
 
Adjusting floats from 23 to 21 mm makes the carbs run RICHER........
Flooding may be as simple as the float "dragging" against a gasket that projects slightly too far into the bowl...(Quite common with aftermarket gaskets)...
 
Thanks for that, but a mixed bag of results this afternoon, but maybe some progress(?)



Only the main jet and tube/needle are transferable from the Chinese carbs to the Keihin, the pilots have a 4mm thread, the Keilin has a 3.5mm thread, but tried the main jet swop.

Little difference.
Decided to put the Chinese set onto the bike with all the jets etc that came with them. Since the cam position timing change this is the first time tried.
Set the needles max weak and ran the bike, not particularly happy and hungry for choke, so too weak maybe,

Re-set the needles one notch off max rich (4th slot from the top) and it ran far better...

At this setting tweaked the tick over down to 1600 with the slides still in sync, but it was reluctant to hold a stead 1600 so a nudge to 1800 ish.

Both sides the same heat and both cooler than ever before. 5.00pm here so getting close to 'Noise Irritation' time with others, so called it a day. Pulled the plug on the RHS and it was black but not sooty, the best colour I've managed so far.

However, if you snap open the twist grip to full throttle the engine almost stops as if it cannot meet the sudden demand for air/mixture.
These Chines carbs are much smaller 'choke' size, the area where the needle is is much smaller than stock. They could well pass the air on full throttle, but only if gradually demanded, so not very good.

However, it is the sweetest it has run ever, so maybe I'm on the track to a set of new correct size Chinese carbs where all the drillings are perfect and the jets reasonably so.
Another observation is the LHS has been and continues to be sensitive to running cooler or much cooler than the RHS, no matter what carb is feeding it. Timing to bias to the RHS?

If anyone has any real world experience of the carbs below fom China, PLEASE voice them here before I spend £70.

https://www.ebay.co.uk/itm/Carburet...del:CB&hash=item4b8bf49523:g:wyIAAOSwLQtgFrpO
 
Saturday morning, and thought I would run the bike and see if it behaves.

Bit of a hard start (ie not instant as ALL other cb175's do on You tube, always in the USA) but quickly settled down while 2K running to warm up and come off the choke.

It settled to a very slow tick over, indicated 1600rpm and both pipes the same temperature, if anything the LHS for once was a touch hotter to the touch at the rear peg location.

Wound the tick over down and now the adjusters do nothing (unless wound in which raises the engine speed) on both sides. This engine cannot go slower.

The pilot air screws do nothing so are both at 1.25 turns out.

Have to say it ticks over a dream, seems like it will do it all day and responds to the twist grip.
Snap open throttle still stops it dead, but if you do a classic twist twist as if to clear it's throat the RHS might sometime back fire in the carb. I have no filters on atm, just fitted them for a trial.

I am tempted to leave it now and see how it is on the road. These carbs are smaller in the choke than the sets sold in China as a pair and I have a birthday coming up in March...so might see if I can have some carbs!



 
I think that user 'Middletons' on this site has experience of the Wincycles carbs, please chip in if you are reading this. (y)

You've probably seen this on Youtube, pity the poster didn't show the bike actually running.

Honda CB175 - Chinese OEMSTD carburetor review - YouTube

I notice that the clone carbs direct from China, rather than the ones from Wincycles in the USA, don't have the OEMSTD logo on the carb body. Just crosses my mind that they might be copies of copies, if you see what I mean ?
 
Yes, understand.
That video I saw some weeks ago, bit disappointing!

They are going to be a gamble, but so were the ones on it right now which are very much a guess if they would work, but the bike sounds great atm albeit on tickover.

however, I have never had the bike running like this ever, though 'on-the-road' could be very different as you know better than me.
I'm not convinced the throat size is open enough on the ones I have, but the ones now on order could be the same or better, worth the gamble.

Once these are on and the bike on off the bench there is only the side stand to fit and then to insure it but I also need to register it as 'Historic' for taxation, hopefully at the Post Ofice.
 
I have indeed used the OEMSTD carbs twice before.

Here’s something to try; grab each throttle cable for each carb and pull up on it. That will rev each carb individually, so you can see which one is the problem. I bet that one is not set right and causing problems.
 
Not sure Ihave a problem to solve on this bike!
It ticks over fab, be nice to try it soon and see if it rides well, but I need to see if these new carbs are better.
At least now I have a set that works so far, so can switch back if all fails.

Exciting times at last!
 
911hillclimber said:
The pilot air screws do nothing so are both at 1.25 turns out.
Click to expand...

This alone tells me there is something drastically wrong.....
The mixture screw passages and jetting are clogged/blocked/not contributing, and/or the engine is already running on the main jetting......

I would completely back-off the "tickover" (throttle stop ) screws and attempt to get it to idle at the prescribed 1250/1300 RPM With just the mixture screws.......
 
What a nightmare you're having Graham! I hope I don't have any carb trouble I've had enough with the loom!

I may be talking out of turn here but when checking float height the carb needs to be tilted so the float JUST touches the float valve. The float valve has a spring loaded pin on it so if the carb is held horizontally upside down the weight of the floats will press the spring down and give you a false height.

Just a thought Graham. Please ignore me if you already know this, as you probably do!
 
Yes, it has never run this well ever.

Today I had another run on it on the bench, I managed to get the tick over down to an indicated 1200 and maybe even 1100 with the filters on. At 1100 the tickover was oh so close to stalling, painfully slow. I am still doubtful of the tacho's accuracy.

With it running, just, at 1200 rpm the pilot screws did nothing when turned +/- 1/2 turn from 1.25 turns out.
These carbs are brand new, so all drillings are clear and the same, the carbs are not handed, so both carbs are machined the same. All innards are the same too.

The engine ticks over better at 1400 easy, would do it all day and the 'breathing' heard at the filter area is the same both sides, the silencers are the same temp in the same spot (by the rear pegs).
The engine instantly starts from hot. The black soot has gone but the plugs are dark.

With the new carbs on the way from Ningbo, China (I used to visit there when I worked!) there is little point messing anymore.

When they are on I can 'save' these current carbs to go with my enviable carb collection! If the new ones fail, then they can go back on.

The stock carbs are past their best. I set the floats just as James says and reset to 21mm from 23mm, so to factory spec. but they never ran as good as these Chinese carbs on the bike at the moment.
I was flogging a dead horse with the Keilins.

Anyway: Why is the tick over tuning so precious? As long as it does, is smooth, and is reliable then all is well? 1400 or 1250 if I try is good. Holding the engine at 6000 rpm the engine is vibrating just as my gold cb175 did, and sounded great.
The engine would return to tickover just like a modern car engine dropping from 3ooo rpm to 1000 tick over.
 
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