Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: keithtraffic on June 01, 2020, 09:10:57 PM
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Sorry - quite a long post!!
As per earlier posts, following major fuel seepages from around the carb bowls and (as it turned out) the fuel tubes between the carbs and also sporadically from the overflow tubes, I undertook to rebuild them.
With help from comments on this forum and Brainj who miraculously managed to supply me with four springs used on the throttle slider link arms, which had been lost during cleaning, the carbs have now all been re-assembled, bench balanced and refitted to the bike - re-fitting them was a nightmare!
During the rebuild the carbs have been vapour blasted and cleaned in an ultrasonic cleaner as well as having all the replaceable jets etc have been replaced along with the seals and O-rings etc. Taking note from others comments I have tried very carefully to make sure that all the internal passage ways were clear and clean.
The good news is that they look good and all of the fuel leakages have been cured.
To complete the exercise I have just finished carefully making sure the timing is spot on (at least statically), the points are good and the tappets are all correctly set up. (Both the timing and some of the tappets clearances were a little bit off).
The bad news is that the bike will not run smoothly at all!
Actually no-1 cylinder is hardly firing - its exhaust pipe is still cool after a couple of minutes whilst the other three cylinders are all hot. just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.
To explore a bit further I did remove the screw where you would attach a vacuum gauge and spray some carb cleaner in and immediately the revs picked and No1 cylinder fired up, perhaps suggesting an issue with the fuel delivery to that cylinder. I have also checked that there is fuel in the cab (by opening the drain screw) and confirmed there is a regular flow of fuel.
Its worth saying at this point that No1 cylinder has always been a bit of a problem in this regard, causing the engine to 'chug' at tickover until the engine has warmed up which makes me wonder if there is possible a more deep seated problem?
I am loathed to remove the carbs again and have another go at clearing them as there seems to be no clear way of knowing if the clearing is successful.
Does anyone have any suggestions - is there anything else which could cause this type of symptom other than the carbs? If I do take them off again what can I do to make 100% sure that all the passageways are clear and there is nothing else causing the problem? Any guidance would be appreciated!
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Thorough diagnosis so far keithtraffic :)
Initial thoughts would be idle circuit on #1 carb as presumably it chimes in if you lift the throttles, and shows it's running when getting fuel via it's main jet?
Worth turning the idle mixture screw all the way in and slowly back it out towards 3 full turns while ticking over to judge the response. This to double check the flow of that circuit.
If no/ little response, try blowing air in via the idle mix port with screw removed ( engine not running) then reassemble to try again.
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Suggests that push in pilot jet or the pathways to/from same.
Last time i had one to do got it running great then it sat 8 weeks and i had to pull the pilots again----i hate pd's and once my box of bits is gone i dont want to see any more
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I agree with Bryanj
My K3 has them on, I've done very little mileage on it and had the carbs in bits three times, it still doesn't run perfectly at all throttle openings, I am about to start looking for the 550F carbs
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I agree with Bryanj
My K3 has them on, I've done very little mileage on it and had the carbs in bits three times, it still doesn't run perfectly at all throttle openings, I am about to start looking for the 550F carbs
Let us all know how you get on :)
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... just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.
How about the plugcaps? Have you tested their resistance? Do caps 1 and 4 show more or less the same resistance? Do you run 'R' plugs by any chance?
Are you sure the idle RPM shown on your tacho are a true 1100?
Also verify the carbs vent. If necessary cut one or two inches of the vent tube(s).
For the moment, this is all I can think of. If I owned a K3, I'd add a small dose of fuel system stuff (or kerosene or lamp oil for that matter) each time you fill the tank.
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To extend the addative theme above, running and looking after very small carburation systems appear to benefit from using two stroke oil with less of that "crystalline" debris accumulation that blocks small jets.
Consider something like a 90 to 1 mix ratio and assses if it reduces the incidence of blockages in these pd systems.
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I have experienced a bit of these woes, as many of the people on here have. I have had my carbs off three times and have found the easiest way for me is to remove air filter box and drop air box collector with intake rubbers attached loosen off 8 m6 nuts from intake manifold pull back and slide out. This is probably not much help but I have juggled between poor or faulty plugs “ngk” and blocked pilots and this was even after an initial complete strip and rebuild of carbs. I remember prior to a complete restoration of my bike I took the carbs off and they were ultrasonically cleaned, made no difference whatsoever probably pilots blocked. Also all four had blocked vents. I now have a bike that runs and ticks over very nicely, in fact I have never had the bike running like this in the 33 years I have owned it. You will get there, (hope it doesn’t take 33 years)! Good luck!.
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My k3 was always ok in the time I ran it - at least carburettion wise, and the first 6 months of that it sat idle while I passed my test. I liked the extra mpg, not that big on shorter trips but stick the bike on a motorway and the economy was great. A roads it matched my mates superdream to the penny on fuel stops, motorway work I could get away with 50% fewer fuel stops. I did find some of the springs on the central cable area and choke return broken when I wanted to put them on my sidecar bike. Not had to resort to redex in the fuel on a k3 but on my wifes 250 nighthawk I saved myself hours of messing around by spraying carb cleaner on the air cleaner and running with redex in the fuel. Took a few weeks commuting before it ran right but I developed a hatred of removing carbs and airbox over the years. Same trick worked with the cb500 sidecar with overflowing carbs.
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When was this ^? Petrol has changed. Even with todays petrol K3s will run fine, provided they ride regularly. Why K3 slowjets are more prone to (partially) blocking then those in the oldstyle carbs? No idea.
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Thanks everyone for the feedback.
Have been 'playing' a bit today to see what happens. I adjusted the idle screw all the way in and then unscrewed it (as suggested by K2-K6). All the way in and No 1 cylinder pretty much stalled but it did pick up as I unwound it (which I think is as expected). I did find that unwinding it too far also seemed to cause the cylinder to get very erratic. I am not sure if I expected that to happen - is that how its supposed to work? Anyway I returned it to 1.5 turns out.
However things do seem to have 'calmed down a bit and I can get the engine to run with all cylinders seeming to be working - at least they are all getting hot! The tick-over is a bit high - 1800 rmp and the engine still doesn't seem particularly happy at a lower tick-over.
I am inclined to take it out for a run and see how things go.
What are the options for changing the carbs to non PD types - is that a viable option?
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That's exactly how it should work if the idle circuit is clean and operating correctly.
You should be able to take it from too rich to run well all the way to too lean to again prevent good running. Tentatively, that appears to show the carb as ok.
Unless you've already tested it, I'd test and record compression for each cylinder next.
Reality check also for carb sync, have you set them with a bench method otherwise referenced on the site?
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I don't have a compression tester (yet!).
Is there a good one that comes 'recommended' Having watched a couple of videos on this it seems that the 'best ones' have their pressure valve close to the cylinder?
The actron cp7828 which was recommended in the video I saw seems pretty expensive from Amazon - nearly £80!
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This one should work ok, but you'd ordinarily need to hold it in the centre cylinders while someone else turns it over for you as it's contorted to do both together.
https://www.mandp.co.uk/products/compression-tester-push-in-type-594478
Usually they have a schrader valve in the end that you push to release, also you don't have to screw anything into the plug threads as some of the kits don't have the correct thread pitch!
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Hi All,
Will need to think about the compression tester, but took the bike out yesterday to see how it performed.
Despite previously reporting that things had settled down and I could achieve a smooth tick over, albeit a bit fast, went out to the bike and started it up and again No1 cylinder was not really firing. Nevertheless decided to give it a run to see if things improved.
The throttle response was initially was pretty sluggish until about 3000 to 3500 revs and then things picked up and the bike really accelerated - like a bat out of hell - actually much better than I remember it (which could be the result of the carb rebuild and also getting the timing correct?).
After a good blast it did seem that No1 cylinder was running OK but then I stopped for a while and when restarted No1 cylinder was again not really running properly.
I am getting the feeling that this is still something to do with carburation but as mentioned before I really don't want to take the carbs off again if I can avoid it. So apart from compression is there anything else I can do as a diagnostic before committing to removing the carbs again?
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Obviously from a remote perspective, but it seems to me that the carbs are doing what they should which is why I feel the need to understand if the cyclinder is ok.
Carbs in situ you could check that you've got decent filling of #1 if you can get the float bowl off. Slow filling would ordinarily give the opposite problem though of reaching level while standing and then depleting while running faster, the inverse of your experience here.
Thinking aloud, if it was overfill while sitting to make it too rich when you start it, then improving as you ride faster, then possibly the fuel leveling out too high in #1.
A question about the carb on #1.....if you get the overflow pipe from that float bowl, can you blow air into the carb? Just clean the end of it and blow with your mouth. Looking to see if there's any impairment to float bowl venting.
Reason for compression test, if you've a significantly compromised cylinder operation then you'll chase the carbs forever and not get it. Psi for each cylinder will at least give a baseline overview to chase or eliminate.
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Thanks - I should have access to a compression tester at the weekend so will check that out (as you say it will help to eliminate one possible area of concern).
I did take great trouble to check that the overflows were working and clear before I reassembled the carbs and great care in ensuring that the floats were set to the right height, but will go round the loop again as you suggest just to make doubly sure.
Does using a clear tube connected to the overflow and holding it up to see what level the fuel comes up to give a proper indication of fuel level on the carbs?
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"Does using a clear tube connected to the overflow and holding it up to see what level the fuel comes up to give a proper indication of fuel level on the carbs?"
No, the internal pipe sits above the normal fuel level of the carbs (essentially like a wier) so that should the levels rise too far they would go out that exit and not run into the carb throat to the engine.
There's usually a screw on base of float bowl that you'd have to connect clear pipe to in order to monitor live fuel level.
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Have now checked the compression after warming up the engine and with the throttle open...
Cylinder 1 165psi
Cylinder 2 155psi
Cylinder 3 165psi
Cylinder 4 160psi
(With the throttle closed all cylinders are the same at roughly 90psi)
So all a fraction low compared to the manual figure of 170psi but I wouldn't have thought the numbers are anything to worry about - and cylinder 1 definitely does not have low compression compared to the rest. I did try squirting in a little oil into the cylinders and that did raise the readings across the board by 20-30 psi.
Another symptom I have just noted is that at tick-over and at speeds up to 2000-3000 revs No1 cylinder is softly backfiring / emitting a sort of sputting sound.
I also tried the trick of blowing into the overflow tube and its definitely clear.
So not sure if this sheds any more light or if really the next stage is to (reluctantly) remove the carbs again and have another close look - is there a diagram or anything of the PD carbs showing all the airways etc and where it should be possible to blow / direct cleaner through to ensure all the fine passageways are definitely clear.
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I'd have confidence in those compression numbers, all appears reasonably in order.
"Actually no-1 cylinder is hardly firing - its exhaust pipe is still cool after a couple of minutes whilst the other three cylinders are all hot. just to be sure this wasn't anything to do with the plus I have swapped 1 & 4 plugs over but to no avail.
To explore a bit further I did remove the screw where you would attach a vacuum gauge and spray some carb cleaner in and immediately the revs picked and No1 cylinder fired up, perhaps suggesting an issue with the fuel delivery to that cylinder. I have also checked that there is fuel in the cab (by opening the drain screw) and confirmed there is a regular flow of fuel"
Before reluctantly investigating the carbs further and reacting to the above, it's worth flipping the coils so that 1 and 4 leads are swapped across the bike to eliminate anything in the number one lead ( does missfire swap to 4) to make sure that's not catching you out. They're obviously fired at the same time but possible to have impairment on one lead and not the other.
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I did think about that but I can't make the No4 lead reach to the No 1 cylinder - is there a quick way round this?
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You'd have to dismount the coils and physically flip them over to facilitate reaching the plugs.
Maybe of benefit though, run it in dark conditions and carefully view the 1 lead closely to see if you have any leakage. You can usually see a spark but also hear one too, like a loose tappet.
If there's obvious spark you can move the lead with a stick to see if the cylinder chimes in. Where they pass rocker cover is normal suspect.
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I will give that a go tomorrow - although I am not sure that would explain the situation where I can spray carb cleaner into the vacuum tube screw hole and the cylinder picks up and runs pretty cleanly (for a second or two).
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Yes was thinking the same as you, that it fires with spray cleaner.
But to explore what's happening, cleaner is much more volatile than fuel mix and will fire with veeeery weak spark. So is it cutting in with cleaner for the above reason (comprised spark), or because it had no fuelling from carburettor.
Guess you could go either way to prove / disprove, one of which involves carb removal :)
I had one recently that took an embarrassing time to get it. On a V8 had similar symptoms of dead cylinder on cold start, chimed in after a while, same again if left for 1/2 hour, exhaust temperature confirmed the cylinder # ended up finding a break of HT lead just inside the rubber boot entering plug cap. You could see a carbon track where the spark was travelling too (not ngk caps) once fixed it's absolutely perfect.
Just another quick reality check, have you swapped the plug caps over between 1 and 4 ?
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Well its all a bit bizarre!
I played around with trying to get the coils off and turning them round but that seemed to be bit difficult in practice and as the no-4 cylinder lead almost reached the no-1 spark plug in any case, I carefully put the coils back in place and fashioned a small 'bare wire' extension, just long enough so it would reach the spark plug from the plug cap, taking care to make sure it could touch any of the cylinder metal work.
But before trying this out I though I would put everything back properly, just to re-check the baseline - and lo and behold the engine fire up and after about a minute was ticking over fairly smoothly - a touch fast at 1600 revs but with no indication of the backfire - and cylinder 1 was definitely working as it got as hot as the others very quickly.
Nevertheless did then swap round the plug leads but this made no difference that I could perceive - so put them back properly again and the engine fired up easily on the starter button with no throttle - and then just sat comfortably at 1600 revs.
So - either disturbing the coils and plug leads has done something or perhaps what ever blockage there might have been in the No1 carb has moved - but I really have no idea which it is!
Assuming the weather here tomorrow is OK I will the bike out again and see how it goes - but any thoughts on the above?
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I agree with K2-K6 ref the maybe a duff lead. I had a break in a lead and worked fine most of the time but on start up and initial slow running, run intermittantly on that cylinder. New coil/leads and instantly cured.
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Appears that you've got the response needed.
Although not absolutely conclusive, it certainly is most of the way to confirming that the HT supply to number 1 is compromised intermittently.
The carbs just seem to work as they should with the response you're getting with mixture screw etc. Your diligent cleaning here seems to have payed off.
Coil 1 and 4 obviously fired by same points so low tension triggering not suspect, but route out from coil down to #1 would be the definite location. If original coils they are extremely reliable, but certainly not infallible.
Wouldn't be a surprise to see it come back though if it's just got it by moving the leads around.
The fact it "chuffs" now and again when cylinder 1 wasn't firing shows fuel is present in the combustion chamber, just unlit and passes into exhaust to be later ignited.
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Thanks for all the help - took the bike out today and generally ok, but did again develop a little chuffing and reluctant No1 after stopping for a while.
I agree tick over at 1800 is definitely too high. I thought the proper figure was about 1000 according to the shop manual?
I have looked at replacement coils and plug caps and they are pretty expensive for original types - over £100 each with VAT for the coils and the plug caps are another £25 each.
David Silver has repro ones at a more palatable £30 + VAT for the coils although they don't seem to be handed (same one for both the left and the right side as far as I can see) - has anyone had experience of these?
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... the 600 was to show that with an engine in fine fettle they will go much lower...
You beat me. Once I was able to have it idling at 800. Not that I recommend it. You want that oil up there. Most bikes of that era wore up there, not at the bottom.
I'm toying with the idea of changing the HT leads to red instead of black, they'll match the NGK caps and look a little different.
Long time ago I went for silicone HT leads and dito plugcaps. Great stuff. At the time there was yellow only. Now even Louis has black.
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Hi Keith. Not that you need to but I’ve used a small right-angled Torx bar with a JIS or Philips driver tip to undo all bowls and remove/clean the main and idle jets with a set of abrasive wires/brushes off eBay, but fiddly!
Re the coils cylinders 2&3 had been slower to warm up.
I bought DSS copy coils and just needed to fit female bullet connectors to I think the yellow adapter leads. There is + and - so note. They then fit fine. Cool screw mounts 11cm apart unlike a set I bought on eBay and returned.
Old ones screws tight to undo. A decent JIS T bar driver useful.
Might be possible to recoup some £ by selling the old coils for refurb.
Other issues, a faulty no 2 plug of all things. Have replaced all plugs with non resistor ones, replaced plug caps with NGK resistor ones, and all working well. CB500/4 K1)
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PS another thought. I think the idle screws may have small holes in them that may get blocked. Not sure but worth checking.
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"David Silver has repro ones at a more palatable £30 + VAT for the coils although they don't seem to be handed (same one for both the left and the right side as far as I can see) - has anyone had experience of these?"
No direct experience of these but they don't appear to draw any significant level of failure comments on here.
They would most likely give you a competant fix immediately though to allow you riding it while running well.
The originals worth keeping for if you decide to repair/ or for someone else to do the same if they wanted originals.
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Yes the DSS ones worked very well for me and fitted fine.
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Thanks - did you replace the plug caps as well - the DSS ones don't come with those?
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Yes the plugs NGK D7EA and NGK resistor caps. 2 long and 2 short with angles at top in black. I’ll try to attach pics. Didn’t cut cables short and outer plugs can point back and in with leads through p clips. Will try a pic of that too
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I prefer 2 long straight on the inner cylinders, far less chance of the HT cable touching the exhaust and it gets them out of the water spray from the front wheel better IMO
Me too. Also I don't like HT leads direct contacting the head. Better to insulate real well!
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Don't know if anyone is doing the same, but I assemble the leads into plug caps using silicone grease which improves water resistance and helps as you screw the cap in.
It's high temperature resistant and I just by it in little tubs from plumbing supply shop.
Edit;- https://www.cityplumbing.co.uk/Polypipe-Silicone-Grease-100g-SG100/p/919370 it's this one I use.
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Good points. I’ll make sure the leads turn up a bit more.
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Actually just checked a despite the pic 2&3 are well clear, but the long straight ones were the original format (?) so good to keep original look (apart from the pressed metal caps maybe!)
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Hi All,
So......
I have replaced the coils (with aftermarket ones for DS) as well as the plug caps (just for good measure as the ones fitted actually look pretty good) and unfortunately things have not improved - same poor low revs performance from cylinder 1 and the slight 'sputting' backfire ae low revs is still noticeable.
It's looking like I am going to have to remove the carbs again to make absolutely sure everything is totally clear and clean - but does anyone have any final last thoughts where else to look before I do down this route - it seems most other things have been tried!
Also does anyone have a decent rubber connector between Carb 1 and the air box - I have noticed mine is beginning to split and an not sure it will survive another carb change (but its not the source of any problems as I have made sure its not leaking when testing the tickover!)
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I think that is the especially unique one due to length and shape, it was discussed on the forum elswhere about a member on US site hand making them
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Re the carb to inlet box rubbers, I managed to get in touch via the us forum and email with the man who is manufacturing replacements, he is very helpful, I got mine delivered in about a week and less than $50 including postage, I'll get his email when I finish work,
PS I am having very similar problems with my bike, I am about to clean the pilot jets for the fourth time which does get the bike running ok for a while, I am on the lookout for a set of alternative carbs as these PD carbs seem prone to issues (odd as they are not particularly complex carbs)
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Problem was then were designed to run as lean as possible for california so any blockage at all makes them impossible
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Let me know if or when they are for sale, if I can have first refusal it will be appreciated
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The email address for Paul Gabor is mybluebike2004@yahoo.com
He responds quickly and is a pleasure to deal with, the rubbers that you will receive are not quite as good looking as genuine ones but not noticeable when fitted, not much choice anyway, the ones from Germany on Ebay are twice the cost and I believe are from Paul
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Ken i will go seconds on the carbs as i dont think i have enough for the engines/frames i have
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I will be honest and say i dont know for certain exactly how many frame/engine combos i have and what bits i am missing
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So, finally bit the bullet and removed the carbs yet again and went through the cleaning process (again) on carb 1, making absolutely sure that that the pilot jet and the passage ways serving it and the mixture screw were definitely clear.
good news! Having now reassembled everything the bike started with the smallest blip on the starter and after a minute or so to warm up was ticking over smoothly, albeit still a little high at 1400 - 1600 revs. But most importantly cylinder 1 was working properly!
I will take the bike out for a run in the next few days to see if everything else is OK, but I guess I still need to set up the idle adjustment properly (at the moment all four screws are just out by 1 1/2 turns).
I am sure I have seen some guidance on the forum for how to do that properly but can't find it now - does anyone have a link to the relevant thread?
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Use it regularly or those carbs will be off again
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... albeit still a little high at 1400 - 1600 revs... but I guess I still need to set up the idle adjustment properly ...
Verify the RPM with a true tacho. I once worked on a K3 and couldn't achieve a nice idle. Then I connected my automotive DMM. Guess what... a true 1000 RPM showed 1400 on the ND tacho. No wonder that when I tried to dial the RPM down to a 1000 on the onboard tacho, it didn't run well. Not saying it is also with yours, but I'd check it.
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That’s very interesting about tacho accuracy, it would explain a lot.
PS re jet etc cleaning I found these pretty good, and used a mini bit holder in situ on the bowls, with some contorting (mini rachet on order)
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Carefull with the wire thingies the pilot jets have a sort of cast in spider for some reason, maybe to atomise better?
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"I am sure I have seen some guidance on the forum for how to do that properly but can't find it now - does anyone have a link to the relevant thread?"
From a Honda manual, set the adjustment screws at recommendation for turns, warm bike to stable tickover off choke, then turn screw on one carb anti clock* and observe engine revs rise (this is where the accurate tachometer comes in) you should reach a peak revs after which the combustion will start to get worse if you keep going. Turn screw back to "peak" revs and then keep going until you see a 100rpm drop ( because you've made it richer) and that's the final calibrated position for that carburettor and jet. ie. You are getting it set to juuust slightly rich of the leanest burn position.
Now adjust the overall tickover with the manual single screw if the revs are too low or high, then work individually through the remaining carbs one at a time.
This routine gives ultimate parity of tick over setup as you'll have just created the same combustion level bespoke to each single cylinder and it's associated carb. The number of turns out should now be recorded as a baseline setup for your bike.
* some carbs are opposite depending if the idle mixture screw is located on engine side of throttle slide or airbox side.
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... From a Honda manual...
What manual is that? It's probably a good method for a 2 cylinder engine. For a 4 cyl. I have my doubts...
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Its in the 750 F2 manual that has PD carbs, not sure about the 550 K3 supplement
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... From a Honda manual...
What manual is that? It's probably a good method for a 2 cylinder engine. For a 4 cyl. I have my doubts...
From a CB 750 "shop manual" dated September 1970 , also still in last CB750 K8 / F2 shop manual too. Both official Honda directions for their technical support.
It's something that's effectively been extended into most fuel injection (both diesel and petrol) systems that evolved, ie. The individual setting of each cylinder demand by calibration of it's slow speed circuit to equal the combustion effort across all pistons. Mostly it's done on the fly currently by monitoring the pulse time of the individual power strokes via crank sensors, and then altering fuelling parameters for the next firing of relevant cylinder to produce smooth idle speed.
The philosophy is the same just faster and more resolved.
In the last 750 sohc manual, it describes this routine as one done at the factory and should remain as a datum point for running the engine. It accepts that the adjustment screws don't have to be an even blanket setting to achieve combustion parity.
Essentially it's saying you can't get an accurate enough setting from the tolerances within the idle circuit just by observing the physical screw position number of turns out from base. In deferring to engine rpm it gives you what you are chasing, even tickover and best combustion parity at that speed from a true calibration routine. :)
It really is the icing on the cake of smooth tickover, which is not vacuum balancing. That doesn't have the resolution to do what this routine does. Although it is a prerequisite of this one that the carb slides are previously set correctly.
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The method itself makes sense. I recommend an analogue tachometer that shows say 40 rpm increments.
Also realise that CB500/550s with old style Keihins need a relatively rich idle to facilitate a good driveability in the lower region, at least in my experience. The K3 is a different story.
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Bryanj yes I think some models have a gauze or something built into one of the jets.
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Carefull with the wire thingies the pilot jets have a sort of cast in spider for some reason, maybe to atomise better?
Not being a native speaker, I don't know what you mean by a 'cast in spider'. Does this pic help?
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Nope, cant expand it enough, if you look through a pressed in pilot the hole does not look "clear" as there is sometning in the small hole and its supposed to be there
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Nope, cant expand it enough, if you look through a pressed in pilot the hole does not look "clear" as there is sometning in the small hole and its supposed to be there
I think I know what you mean. I have the same experience, but in my case I'm sure it's caused by my own eyes, a trompe-l'oeil if you will pardon my French. To verify the slow jet is clear, you need a magnifying glass, then vary its distance to the jet a bit until you see a hole like in the pic below. I can only see it using a magnifying glass or... by taking a picture. When you see a perfect round hole, you can be sure the bore is clear.
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Using the stainless wires VERY carefully I found the smallest ones went through one or two of the (Cb500) pilot jets with ease, no sign of obstructions, but some had a chalky white oxide type build up, similar to that in the float bowls. The wires are slightly abrasive half way along and went through the unblocked ones ok, so I felt I could risk cleaning the blocked ones to a similar level. It now starts and runs well.
Probably very close to 40# but likely old ones that have had any deposit will be slightly coarse and tend to attract more deposits. In hind sight with all the work involved new pilots would be tempting and the excellent forum members supply some good ones I think.
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... some had a chalky white oxide type build up...
It's residue from water. Decades ago I found it in some of the little holes in the needle jet sides. I cleaned them... never noticed any difference. ???