Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Sesman on August 21, 2022, 11:22:35 AM
-
Just thought I’d share my experience with an issue on my recently restored 500 four.
Although I’ve owned the bike for a year or so, I’d not really ridden it seriously….just a quick trip round the block. I’m preparing the machine for sale and was intent on ensuring the bike ran perfectly. I’d noticed that the bike was fine on choke, but wouldn’t idle correctly and responded poorly to blipping the throttle, noticeably hanging and failing to settle properly. Naturally I suspected the idle circuits. I’d previously checked all other influencing items such as leaks, timing valve gaps etc, etc.
I removed the idle jets (#40) soaked them in STP carb cleaner and blew them out with an air line. Interestingly I also aerosoled the jets and it was clear they were passing cleaner under pressure. I reassembled, but the situation was the same. I dismantled once more and this time viewed the jet through a bright back light. I could see clearly what appeared to be a translucent, spiders web type structure that would not allow a .4mm wire probe to pass through .
In an attempt to clear the hole, I heated the jets then plunged them in cold water. I prepared the wire probe by cutting it with pliers to create a small cutting edge, inserted the wire and rotated until the wire passed through, then blasted again with aerosol cleaner.
Result: impeccable tickover and throttle response….
I was nervous about passing wire through the jet, but it clearly had the desired effect and removed the obstruction. All four idle jets were affected identically in the same way.
Just thought my experience might help others on this forum. If you use this method, ensure you use a wire gauge slightly smaller than the jet drilling size. I used .4mm on a #40 jet and it worked just fine. But it might pay to break up the obstruction with a .38mm in. #40 jet….who knows.
-
The spider creates a vortex so droplets don't form ( the spider creates a mist) . It should be cleaned but not removed ;)
-
Interesting that Trigger. The bike didn’t run properly at all until I’d cleared it with the wire!
Or are you winding me up…..😉
P
-
Interesting that Trigger. The bike didn’t run properly at all until I’d cleared it with the wire!
Or are you winding me up…..😉
P
No, i am not pulling your leg. If it was not running right then, the hole or spider was dirty. Destroying will make droplets and it will run rich. From memory the bike will miss behave at higher revs. The spider is there for a reason ;)
-
That’s really interesting Trig. I thought the pilot jet was all but redundant on rising throttle, being superseded by the slide cutaway, needle then main jet. Another school day it seems.
Strangely the bike runs absolutely fine all the way through the rev range. Just returned from a 30 mile trip and the plugs are perfect. Looks like I’ve done a wrong to achieve a right!
I’ve no doubt there is a reason for the design and I’d love to know how they create that finite bit of engineering during manufacturing.
Thanks for the info.
Regards
P
-
Incidentally, I’ll replace the pilots with new replacement just for peace of mind. Would you know where I might acquire 4No new ones?
I see Allan’s have some, but I’m a little unsure on the specification. Are the cb 500 4 the 28mm type?
-
Interesting. I wonder if anyone has a close up photo or diagram of these structures? It never occurred to me when I cleaned mine. Some were blocked solid, so an ultrasonic cleaner would be needed?
Also wondering if this could cause a stall at tickover when hot.
-
I’ll attempt that when my replacements arrive, but to be fair the bike starts and runs like a new one. I’d love to know how they manufacture them.
I suspect that by clearing the ‘web’ the engine will run slightly rich at tickover and this may contribute at high revs to a slightly richer mixture …but I’m absolutely no authority on the topic.
I’ll know soon as I’m anticipating that with new pilot jets, more choke may be required for cold starting….we shall see.
-
It’s possible that if the webs were creating a mist, fuel droplets and an over rich mixture would create a hot stall….just guessing. The air screws can only do so much in terms of vernier mixture adjustment? I’m guessing that it’s the combination of fuel delivery and air screw adjustment that’s important and by clearing the webs ( if they really exist) it’s possible to wander off scale too far.
But again I stress, if I’ve mistakenly removed the webs thinking they were some kind of blockage….my eyes are not good….i’ve not suffered any noticeable detrimental effects…so far.
-
Interesting. I wonder if anyone has a close up photo or diagram of these structures? It never occurred to me when I cleaned mine. Some were blocked solid, so an ultrasonic cleaner would be needed?
Also wondering if this could cause a stall at tickover when hot.
-
Thanks deltarider.
Where would that spider structure exist. Or is it simply an optical illusion brought about by reflections at the drilling junction?
-
Wonder if I’ve just spent £28:on replacement pilot jets for no good reason.😭
-
Both 500 and 550 use the same pilot jets.
Even when my eyesight was perfect (and I had exceptionally good eyes when younger, still not bad now) I never saw this spider web on the inside of those jets, I've even done what you did and used a piece of wire to clean them out and never noticed any difference in how the engine ran.
-
Mmm, me thinks Trigger is taking the piss……
-
There is no spider web structure. It's an optical illusion. http://www.sohc.co.uk/index.php/topic,22417.msg204301.html#msg204301
-
Very many thanks. Good to understand. I get some plug sooting but probably a combination of general wear, valve guide seals, and jets worn slightly oversize. It seems to be getting better with more decent longer runs, but fresh jets would be a nice treat in future.
-
FM. Judging from that historic post it’s still unclear.
Personally I very much doubt the jet is more than a simple drilling, unless somebody would care to produce evidence to the contrary.
-
Very many thanks. Good to understand. I get some plug sooting but probably a combination of general wear, valve guide seals, and jets worn slightly oversize. It seems to be getting better with more decent longer runs, but fresh jets would be a nice treat in future.
The carb needle jets wear out far quicker than other jets due to needle vibration from the engine when the throttle slides open and close.
Most people ignore them and waste cash on the easy to change jets instead, just like I did with my CB750.
New needle jets instantly cured my lumpy slow running and sooty exhaust problems.
You probably require 1601-232-3004 needle jet kits X 4.
Not cheap for a CB500K1 tho...
Good luck
Skoti
-
I have about 3 sets of carbs apart right now. I'll check all the pilot jets to see if any show any sign of ANYTHING down inside them.
I do think some jets have this feature just not these, the small holes are meant to be the atomisers for the fuel.
-
Cheers Oddjob.
Looking forward to the outcome.
-
Well.
Checked 2 sets of jets and there is something in there. At first it's not really apparent but when you look through the jet whilst holding it up to an intense white light like an LED you can see what looks like a * in fact that exactly how it looks, 3 lines intersecting in the middle. I checked a set of 069a carbs and a set of 627B carbs and both show this odd little feature. I have no idea how they manufactured them like that. Probing the jet with a piece of wire off a wire brush they all felt the obstruction in exactly the same place, you can actually get the wire down past it by wiggling it a little but the obstruction is right where the body and the narrow tube meet. I measured the wire and it's right there on all of them.
I doubt a wire would break these lines but a drill certainly would. Not wonder my probing with a interdental brush didn't work when I was cleaning these jets. I thought maybe the brushes were too big but it's just that they are too soft to break the mesh.
-
Now perhaps Trigger is not taking the piss.
I managed to probe through with a 0.4mm wire with some effort, obviously clearing the ‘web’ as I’ve come to describe it.
I’m about to remove a new OEM jet I bought last year for the 550……sound of drums slowly building.
-
And the winner is……
Brand new #38 jet for the 550. A 0.2mm and 0.3mm wire passes straight through.
I’ve had a good look through a bright light wearing sunglasses and I’m convinced it’s an optical illusion…light refraction.
-
Very many thanks. Good to understand. I get some plug sooting but probably a combination of general wear, valve guide seals, and jets worn slightly oversize. It seems to be getting better with more decent longer runs, but fresh jets would be a nice treat in future.
The carb needle jets wear out far quicker than other jets due to needle vibration from the engine when the throttle slides open and close.
Most people ignore them and waste cash on the easy to change jets instead, just like I did with my CB750.
New needle jets instantly cured my lumpy slow running and sooty exhaust problems.
You probably require 1601-232-3004 needle jet kits X 4.
Not cheap for a CB500K1 tho...
Although needles worn by bibrations is known for one and two cylinder bikes, I have yet to see the first needles worn by vibrations on a 4 cylinder bike. Vibrations on a 4 cylinder are very very little indeed.
-
I've seen visibally oval main jet needle seats on SU carbs regularly on cars - more so when BL spring mounted the main needles on later designs.
-
There’s definitely a spider in there I can see them in both sets of f2 carbs I have but only when I take my glasses off
-
Bet you can’t. Try passing a 0.2mm then .3mm wire through a clean jet. If it goes through, there is no spiders web.
-
It might not be relevant but back in the 1960 blocked jets on Vauxhall Vivas caused misfires due to them blocking up - the factory fix was to produce similar jets fitted with a screen filter as a remedy.
Eventually they just fitted better in line fuel filters that fixed the issue completely.
-
Bet you can’t. Try passing a 0.2mm then .3mm wire through a clean jet. If it goes through, there is no spiders web.
exactly push any wire through and there will be no spiders web left I know what I can see in my jets it’s definitely there 😊
-
"I've seen visibally oval main jet needle seats on SU carbs regularly on cars - more so when BL spring mounted the main needles on later designs."
Ted makes a interesting observation regarding oval wear on needle jets because it's apparently not only engine vibration that wears them but also the inlet vacuum effect.
When accelerating hard on full throttle the vacuum draws the needle forward hard against the needle jet and then the back and forth motion causes this oval wear pattern which was also evident on my CB750 when I changed my first needle jet set at 24k.
It's obvious that I'm not the only one on this forum that worked in the motorcycle trade in the seventies or others who perhaps professionally repair that stuff nowadays so to them please forgive me for offering this advice.
The needle jet and needle control the correct amount of fuel passing through the main jet up to about 3/4 throttle opening, after that the main jet size defines the correct fuel supply.
My point is that no amount of fiddling with slow jets will considerably alter rich running problems on the road as the slow jets only controls engine idle and the transition to the needle jet and main jet fuel supply and is effective up to around 1/8 throttle opening.
Worn needle jets alter the air/fuel ratio and cause rich running and possibly throttle hanging etc.
Damaged slow running jets enlarged by cleaning with oversized wire probably won't improve things either...
Please correct me if you think I'm wrong, I'm never to old to learn!
Regards
Skoti
-
Bet you can’t. Try passing a 0.2mm then .3mm wire through a clean jet. If it goes through, there is no spiders web.
exactly push any wire through and there will be no spiders web left I know what I can see in my jets it’s definitely there 😊
No not really. I’m not talking about pushing or ramming a probe….just passing. Until somebody shows me physical evidence I’m convinced it’s an optical illusion due to light refraction at the drilling reduction.
-
Incidentally, if the ‘imaginary’ structure in the jet could not resist light pressure from a soft wire, it could never withstand the persistent pressure from a changing vacuum strong enough to vapourise fuel.
Being a pragmatist, I tend to only believe what I can observe and a 0.3mm wire effortlessly passing through a 0.38mm new jet tends to suggest my observations are accurate.
My jets are squeaky clean and the bike runs perfectly.
I’m not saying your jets don’t have some kind of sophisticated internal structure, I’m just saying your analysis may be flawed…visually.
-
I take on board the idea of the web being an optical illusion BUT all the probes I did were halted in exactly the same place on every jet. I measured the wire and it was identical from either end, they all showed some obstruction where the diffuser part met the threaded part. The wire was thin enough to pass through the obstruction IF you wiggled it but not if you just pushed.
However this could also be caused by how they are machined, if the upper part (the part stamped with the number) bores are larger than 40 size and only where it meets the lower part is actually drilled 40 that would mean a small step where the larger and smaller bores meet (you following me) this could be the obstruction, it hits this step and you feel it must be the web, a little jiggling and it finds the smaller hole and passes through. Which could mean the web is an optical illusion. I mean in the pic showing one dissected there doesn't appear to be any sign of the web BUT I can't zoom in on those pics so maybe it's there but too small to see?
-
I get the theory as to why they might be there but cant for the life of me sort out in my head how they would manufacture them to such a minute tolerance in such a small area. Surely that's impossible to cast (think they were machined from solid) and even more so to miss whilst machining the insides, irradicating it before completion.
I had a good look in all the old Honda jets I've collectedover the years and some are for the 550 but I've nothing in mine but easy to get the results as per your description.
Not saying anybody is mistaken and always bow to superior knowledge but finding this a bit hard to work out mentally!
Nothing new there I hear the masses shriek! :D
-
Folks, I hope I can convince you, there are NO structures in there. Numerous times I've thought there was a web. On all occasions, just by changing my distance in POV, I came to the conclusion there wasn't. Only you need either glasses or a magnifying glass and you need to vary the distance. The pic below was taken right after I thought there was a web. I did NOTHING and just made a pic. See for yourself. Besides, what use would a web have there? I mean, not even the main jets have one. Please don't allow the hoax to be the next nonsense story. We already have plenty of silly claims in the international forum which I've tried to fight for years. Some are very persistent because Mr. so and so made the claim and not many dare to contradict him or even ask him to clarify.
Here's a question though. The first (and only) time I've pulled the float needle valves from their seats, I remember I've seen in there a very thin, almost felt like gauze or was it mabey very thin aluminium? Some sort of filter? I'm not sure. Maybe I was misled and was it just collected dust. Has any of you seen what I 'saw'?
-
All. I think the difficulty getting a wire through is due to the significant step in the drilling. The step is present on both sides of the jet. The .38 or .4mm drilling is very short relative to the length of the jet (28mm).
Iv’e now inspected several old original, new original and new pattern pilot jets and arrived at the same conclusion….it’s a drilling only. I’m not convinced any kind of engineering intervention within the jet is required to effect correct running…..I’ve proven this empirically. Unless somebody can demonstrate it’s possible to pass a .3mm wire past the mythical spider in a .38mm jet it doesn’t exist. In my mind at least.
Show me the spiders web….
My visual observations to date have simply observed the refractive effects at the internal drilling step. Try viewing the end again with a wire inserted….you will see what I mean.
-
Ka Pow!
I'm in no position to question on things I know nowt about but I've found this really interesting from the off. In my addled head I couldnt fathom the manufacturing process involved in the making of the jet to allow the web to be present. It simply didnt compute for Honda to manufacture such a fiddly scenario, no mtter what technology they held at the time. I'm not sure you could do it now tbh, happy to be enlightened though.
At the end of the day, this has been a really good use of brain cells to conclude an issue/topic/myth or however you want to lable it. This is what the forum's for and just emphesises what a great thing it is to be involved in.
Disclaimer: I dont get any form of commission from SOHC and not a 'crawly bum lick' either, just highlighting what we already know ;);D
-
Wasnt Honda that made them, they bought in carbs from Keihn who made for lots of manufacturers
-
Just read this whole thread and with my none Honda engineering background, my logic says this debate hinges around how the spidery web structure could be manufactured - if it could, then there can then be a debate as to its use - if that structure could not be engineered, then the discussion ends? Original post where the bike runs well after clean out seems to be the proof of the pudding in the absence of this?
Sent from my moto g(50) using Tapatalk
-
Incidentally, to close this out. I replaced all four pilot jets with new replacements…..it didn’t change a thing and the bike performs just like it did after the clean…..perfectly. I can now go on to check sync the vacuum, but to be fair it seems fine. It might quiet the clutch down a little, but as it’s a 500 I’m doubtful.