Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: fogrider on May 27, 2021, 06:21:21 PM
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Looking at carb kits for sale for the CB550f, there seems to be two types : an air screw that is solid paired with a long idle jet, then a hollow air screw with a side hole in it as well with a smaller bodied idle jet. My 1976 F1 has the solid air screw pairing and as I cannot get rid of the huge bogging down just above idle, I wonder if they are the right ones ?
I have done all the usual things - points/dwell, ignition timing, advancer OK, fuel level Ok and it idles well and reacts to air screw changes. It's not too bad after several miles and warmed up, but from cold it just won't play off idle without full choke but then, after clearing up and revving OK it ,obviously, goes way too rich.
The carbs have been stripped and cleaned ( they were OK as it happens ) but I seem to be missing something, probably obvious !
Any pointers very welcome.
Regards all, Terry.
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The solid type airscrews and the long jets are the right ones for your model. Genuine Keihin jets have the star like K logo stamped. You may want to consult the overview attached. Generally speaking the chokes will be fully opened again before departure but you will need a raised idle for the first two km. Some keep the grip twisted for this, as suggested in the Owner's manual, others use the big idle adjuster which they readjust at say the second traffic light. Do not expect a good acceleration from a stop with the throttle yanked open more than halfway.
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That's excellent, clears up the thing about hollow tip and solid. It runs as though a smaller cutaway would be better but they're original and in good order. Honda knew best I'm sure.
I spotted a reference to fuel levels later last night, someone had checked with a clear tube - 3mm below fuel bowl top.
Might have a look at that out of interest.
Thanks Deltarider, very useful info.
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To verify correct fuel levels, you may want to use the simple method.described here: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647
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The solid type airscrews and the long jets are the right ones for your model. Genuine Keihin jets have the star like K logo stamped. You may want to consult the overview attached. Generally speaking the chokes will be fully opened again before departure but you will need a raised idle for the first two km. Some keep the grip twisted for this, as suggested in the Owner's manual, others use the big idle adjuster which they readjust at say the second traffic light. Do not expect a good acceleration from a stop with the throttle yanked open more than halfway.
The information is incorrect: keihin air screws can come with or without holes ;)
[attachimg=1]
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Can you show us where that was denied? It's my habit to post all information thus that it can be falsified by anyone. So far I have not received additions/corrections concerning the carbs. overview, nor the method for verifying fuel levels. I'm always open to it and will be happy to add or correct anything when needed.
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My idle screws look as old as the carbs so I assume they have'nt been changed. It ticks over fine too so it looks like the solid ones are correct.
Have done the clear tube fuel level already, between 3 and 4 mm so possibly OK. Like your drain down quantities check idea, cup of tea and next job !
I can't find any reference to what cutaway these slides are, I'm sure a smaller cutaway will cure it, but what's the original ?
Regards all, Terry.
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As already mentioned, they can be quite cold blooded from that period as they started to grapple with emmisions focus that was more related to fuel supplies and oil prices etc.
Where have you got the airscrew set? It can be beneficial to go a more little toward rich than what you'd consider ideal. It brings the idle circuit up sooner as you lift the slides and may just be enough to encourage more smooth transition. Worthwhile to do a comparison.
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"I can't find any reference to what cutaway these slides are, I'm sure a smaller cutaway will cure it, but what's the original ?"
As far as I'm aware there's no alternative slide cut available, but agree it would be something the could clean this area up by inducing raised initial vacuum just as you open the throttle.
One way of moving it slightly that way would be to go one size (smallest step) up on idle jet, then you'd have to run with the airscrew further out to stop tickover being too rich but get quicker ramp up in volume as you start opening the slide. Potentially the opposite side round the same square to changing slide cut.
Something they appear sensitive to also, some markets had different airbox cover I believe that affect carburation and so worth checking for oddity there.
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Thanks for that latest, I have tried a richer idle setting and it did make a small difference, at least it demonstrated that that is where the issue lies.
I have thought about turning a half mill off the bottom of the slides then packing the needle up the same . It's a no going back step !
Dare I do it ?
Must price some slides up to see if it's worth a gamble.
By the way , I tried Deltariders fuel drain check, 50cc per bowl result. Looks like fuel levels are OK.
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I'd look at the slide question like this;- effectively you're trying to increase the vacuum at lower slide position to pull more fuel through the existing idle jet specification, balanced by the air jet for mitigation.
And so, if you increase the idle jet size, then the same (existing vacuum) pulls against less resistance in drawing fuel up from float bowl, again mitigated by the air screw setting. In essence the same or close to it as changing the slide, but reversible ultimately.
In addition, if you drop the needle one notch this too would subtract fuel that the idle circuit adds higher up the range. Ultimately it should "fatten" just the transient above idle response while leaving the rest alone, which is what it appears to need.
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Dont think ive ever seen slides for sale
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CMSL list them, 73.5 eur each plus plus. They list USA and UK , same part number . Not shown at Silvers.
Looking at ebay, there are Keihin slides quite cheap in the USA, but the adverts don't make it clear exactly what they fit. There is a choice of cutaway though, which looks promising.
Work in progress, someone somewhere has some, but I'm determined to try a smaller cutaway. I'm sure it's the answer to this seemingly common problem. !
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Before you undertake drastic measures, could you inform us some more like on air intake? Pics are welcome. I think it's odd you need full choke at first and then, when warmed up, engine bogs down. IMO something is not standard. Are you sure brassware is original, that the little O-rings around main jets are still OK and seal well? Is airfilter element OK or has it been wet?
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You say cmmn problem but not one ive come accross ona factory standard bike
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I've seen a few references to it on these forums which makes it appear as a known issue.
It does not bog down when it gets hot, it bogs badly from cold , choke eases it ( then gets too rich and I have to take choke off so it bogs again. ). Perhaps I explained that badly.
Get above 1/3 throttle even when cold and it flies. Runs much better once warmed through , but it takes a few miles. All brass wear is good, new float valves and main jets plus all O rings. No leaks. Fuel levels proved correct.
I've decide to fit my lambda sensor kit tomorrow, just after the 4 into 1 and see what the reader says , that should be interesting.
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There is smething ese wrong with it somewhere as that is not ormal and carb slides dont alter
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Best advice I can give, is to start from as stock as possible. Consulting Honda docs can be a great help, but... not when there is an error. You may read about an error in the page that deals with the initial carb set up. A German discovered this not that long ago. The correction he made, has already helped others. http://forums.sohc4.net/index.php/topic,184299.msg2133957.html#msg2133957 Not saying it is the cause, but the position of the slides - and thus the cut outs - is involved, so it wouldn't hurt checking you have the correct initial set up. It's quickly done.
A further addition. Don't make the mistake in trying to achieve a highest rpm* at idle by turning the air screws out. It is possible and the engine will pur like a kitten, but you will have a rotten acceleration. These CB500/550s need an idle mixture that is on the rich side, which - strange as it may sound - could imply having the slides a bit higher.
*This may be the correct procedure for other carbs. Ours are very basic and lack acceleration jets.
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As far as I know, it is all standard and the carb settings right, including the 49mm thing. Idle screws down to 1 and 1/4 turns out.
I only bought it last October and the wiring mess was the priority and this year I set to re-painting the tank and side panels
so hardly ridden 'till recently. When I stripped the carbs to check the internals it seemed strange that the carb slides looked as new. It was off the road a while after the last owner died and someone since has re-built the wheels and I wonder if it's also had new slides - the wrong ones ?
It's remains a mystery, whatever I've checked or done.
Before I go overboard with slide mods, I checked the voltage to the coils. It revs free in neutral but bogs (when cold) on the road. That is typical of ignition faults and sure enough, there is a loss of 1 volt with the ignition on (but with the coils disconnected). No lights on. Some drain somewhere ?
It's still got the old type of reg and rec , I might try new , Podtronics OK ?
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As far as I know, it is all standard and the carb settings right, including the 49mm thing. Idle screws down to 1 and 1/4 turns out.
Try 11/2, 13/4 and 2 turns out and see what it does.
... it seemed strange that the carb slides looked as new...
So do mine and they are 45 years old.
I checked the voltage to the coils. It revs free in neutral but bogs (when cold) on the road. That is typical of ignition faults
Really? ... and sure enough, there is a loss of 1 volt with the ignition on (but with the coils disconnected).
I'm afraid I can't follow you here. If you mean onboard voltage drops 1V when - with IGN key ON - kill switch is switched from OFF to RUN, that's not abnormal.
It's still got the old type of reg and rec
Good, keep them, they rarely fail. Recently on the German site someone proved his stock regulator is actually better than electronic as it compensates somewhat for temperature, which none of the electronic ones do, not as far I know. , I might try new , Podtronics OK ?
Don't.
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Opening the air screws makes it worse. It starts to spit back in the air box even worse.. I started to suspect the cam timing in case someone had replaced the chain and it was slightly out. It's absolutely bang on.
It still all points to weakness and after marking the throttle grip, the bad spot is well before 1/4 open. It's a real flier once it's above 3000 rpm ( for 50bhp anyway ) and past 1/3 rd throttle, nothing wrong with the engine. No backfiring on the over-run.
Having another scan of previous similar posts, someone in New York (I think) -Nordstudio- had exactly the same problem in 2009. The thread stops before any cure is stated. Typical.
My son thinks it's the Jama silencer, can't see that, it goes too well. Unless others have had issues with a Jama ?
Sick of it for now, it's going under a sheet in the corner and the T150 is coming out for some fun.
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I view it that there's no particular ideal for airscrew setting, wind it down to only 1/2 turn out and it well tell you something at least.
If it covers it off then that's really telling you that it could benefit from one step up in idle jet size with the screws in more conventional range.
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Thanks K2-K6, I have tried all ways with the idle screws. When screwing in, at less than 3/4 turn out it starts to kill the engine and I have to turn back out to at least 1. It won't wear 1/2 a turn at all. It ticks over quite well at 1 and a 1/2 turns out, at 1 and a 1/4, when fully warm, it's almost sorted, just some hesitation bottom end which is a pratt in traffic.
That reminds me of a classic Citroen dealer in Germany I buy parts off. In their very elaborate parts manual, ( English translation ), there is a description of "the enjoyment the boss gets out of screwing." I rang him and asked what it meant. When he said working with the tools and the fasteners, I explained what screwing meant in the UK.
It went quiet for a bit, then laughter.
I'll sort it, eventually, it goes too well to be anything expensive.
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If you want to try something that runs against conventional thinking, you can use resistor spark plugs and plug caps together and gap the plugs at the absolute minimum of specification in the manual.
I'm intrigued as to this and if it makes a difference both positive or negative on other's engines. My experience is that it's effective with leaner mixtures and helps to avoid it going toward a flat spot without forcing mixture rich to achieve it.
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I get the idea, but when I bought the T150 it was a git to kick off. I found it had resistor plugs and 10k ohm plug caps.
I got 5k ohm caps and non resistor plugs and it became easy to start. ( it had copper leads already ).
I've tried the plug gaps at 30 thou and down to 24 thou. Could'nt tell any difference although the sparks do look poor, pinky/purple not blue, but it pulls hard, even in top, so my thought a weak spark was letting it down did'nt pan out.
I've spotted an issue with the timing marks I'm going to investigate. It's possible timing errors may be upsetting carb synch and settings.
It came with a simple foam liner instead of a paper element filter, I see some people run pods without a problem but it might be a small part of a joint enterprise in upsetting the running.
Work in progress.
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Pods are always a problem and the "simple" foam filter may just be altering the airflow enough to upset the running
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You're right, I'm just checking and eliminating what I suspect and ensuring all is correct. There had been a lot of poor work on it, neglect, bodgery even ,so I don't know what's been done until I dig into it. Lots of little things together can add up. Making the slides slightly richer is a last resort, as you say, it should'nt need it but if that's what it takes......I'll try it even if it's just an experiment. Last resort.
When I finally cure it, it will be the most comprehensively serviced CB550 on the road !
Had a look another look at the 56mm/ 49mm thing while the tank was off (again). I had set mine at 56 whilst the carbs were off , it's not critical, simply puts the cable crank in the right field, hence the 3mm allowance. The German guy simply measures it from more obvious points. The measurement is point to point too, I notice someone on here was measuring it 38 mm, but was being mislead by the lines added to the photo. It was probably right point to point !
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Presumably T150 is a Trident? Can see your point there regarding mixture. These 550 are probably exactly the opposit and bang on the money for AFR with any error likely to be toward lean if any compromise is present. Generally extremely accurate for fuelling and run well through their rev range.
Agree with Bryan's view regarding foam filter, they are certainly sensitive to any shift within intake system and many struggle when using pods.
Interestingly, pods in my view seem to need different cut slides, which ties with your perception now. Probably a good move to asses with original type air filter to see what you get.
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Pods are always a problem and the "simple" foam filter may just be altering the airflow enough to upset the running
Couldn't agree more... (had a recent episode with a CB600F PC36 which was garaged for 3 years and wouldn't fire "...just needs carbs cleaned..."; yeah... all cleaned and bench synced it fired up nicely, but bogged on throttle... sports-filter out, OEM paper element in, and what you know, reving promptly and smooth...)
OEM setup seems the best, as it's just working under all given conditions...
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Air filter element and 4 spark plugs being ordered tomorrow. The plugs look OK, but who knows how old they are, won't hurt to have a spare set if they make no difference.
Made some experimental changes to the ignition set-up , had a ride around , definitely improved and even my non technic wife said, on return, "that sounded way better".
Hopefully, an air filter may just make the final difference. Should have spotted it was'nt a pleated paper one sooner.
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The 500/550 respond incredibly well to getting the points gap and static timing spot on, this can be very frustrating to do but is worth getting spot on F with a 0.35mm gap
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Quite so. Mine ended up at .32mm which gave a dwell of 50%, done static then checked with dwell meter and the strobe and it's all now bang on. Just the carb synch to re-do since having the carbs to bits again. Regarding the timing, the F mark is at 5 deg. Very short for a hemi head. I rotated the backplate until it ticked over best. That was about 12 deg btdc. As that would put max advance too high, I re-set the advance stops to 34 degrees, ( factory worked out at 33). It runs way better bottom end and starts easier. As they are fully advanced at 2500 revs, ( how much time riding less than that ? ) no harm can be done and it goes better, it was an experiment but I'm leaving it like that.
New plugs and a proper air filter should ,hopefully, make the final touches for perfect running.
I still think the sparks are weak, ( pinky /purply ), work in progress, but the improved smoothness makes it much more pleasure to ride.
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As it is put in the trade " they are all like that sir"
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That's good to know - I can forget looking for the fat blue thing now !
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Something strange in that you've advanced timing to improve starting. It's an area they are never usually compromised in and notable for just very easy instant starting.
Being a "hemi" or semi-hemi :) as they don't use much piston dome at all, they don't seem to follow convention for that arrangement as recognized by other non Honda applications. If static advance is producing better result then it suggests something isn't quite right as they don't generally need much spark "lead" to run effectively. Have you checked compression yet as that may give more insight.
Giving extra static advance will usually pull up the idle rpm on engines, which has to be countered by having the throttle slides lower to hold onto revs. It may give you an unexpected effect as you go from overun with throttle closed as it pulls raised vacuum against the slides that makes them harder to modulate in that initial phase as you try to bring the throttle back up on entering a corner for example. You could see it just at that point in erratic off on effect.
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OK, it's not a usual thing to do, but it likes it, no side effects, just runs better. I think it confirms the mystery weakness at the bottom end. All 4 plugs are identical colours so whatever is causing that weakness is built in, not like one faulty carb.
I altered the slides to 2.2 from 2.5 and there is hardly any difference. I'm halfway through fitting the Lambda sensor and reader. What that shows will be very interesting.
Next few days.........
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It'll be interesting to see the results of AFR monitoring, I like investigative things to clarify what you are getting.
Flat spots are always going to be a "non burn" or partial of the combustion content, and usually too lean. Maybe getting close to 14.7 to 1 or just over during that acceleration phase.
The compression would add more to the analysis I feel, especially if it's stood for some time as the rings are often stuck on examples seen here.
Maybe worth running with the breather pipe submerged in a glass of oil too as they can suck air from crankcase on induction stroke to give unmetered air content in cylinder. It'll draw the oil into the cases if it's got poor sealing.
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Lambda sender fitted and have had a run about. When fully warmed up, stopped and read the idle, slightly rich. ( on return, I turned the air screws out to between 1 .1/2 to 1.3/4 turns out from 1.1/4 which now reads right ).
Shocking to see that from even the slightest opening of the throttle right up to half open, the weakness was off the scale.
From half throttle on, goes well rich ! I had bought an aftermarket carb kit, fitted the float valves as mine were shot, left the idle jets in, left the needle jets/emulsion tubes in but fitted the new needles. Fitted the main jets as they had new O rings on but were marked 98, whereas the old ones were 105. From the results, I can only assume there is a serious discrepancy with those needles ( in clip 2 the same as original ) and there is almost no transition from idle to needles via the slides.
I'm sure the mains should be 98, had someone already put 105's in hoping to cure weakness ? or is it just the new needles ? Carbs to come off again, old needles back in. Test run again next week.
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Afterarket needles are notoriousy inncorrect in both diameterand taper, clip position is usually middle and i thought mai jet was supposed to be 100
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His is an 'F' that had 98. Below an overview of the oldstyle carbs on CB500/550. Feel free to comment and/or suggest corrections.
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That's a useful chart, great details and part numbers, only missing the cutaway, mine are 2.5 for the 069a and genuine Keihins. Not sure about the others.
Looked at the old needles, correct part numbers. I'll have a critical comparison of the aftermarket ones, once I've got them out. Sincerely hope that that's it.
Regarding it going very rich top end, will have to check the hole size in the new mains, maybe they're duff too. If these latest changes cure it, I should be able to go back to standard ignition.
Had a belt around Notts and Lincs on the VFR for a day out, nearly 200 miles , a couple of great cafe stops, lovely cake in Tiggys in Epworth. Great ride out with an ex bike cop on his 1300 Pan.
Made a pleasant change from tinkering.
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... only missing the cutaway, mine are 2.5 for the 069a and genuine Keihins. Not sure about the others...
All CB500/550s have the same slides/cutaway.
... Regarding it going very rich top end...
Expect to need 6% CO, to have it run right.
I don't know if you have the Shop Manual and in particular the CB550F addendum. They're here in a good resolution: https://www.dropbox.com/s/88zdzlj8olqi8pl/Honda%20CB500_CB550%20%20Four%20Service%20Manual.pdf?dl=0
As for the various CB550 Parts Lists, they're all here: http://www.honda4fun.com/materiale-documentazione-tecnica/parts-list/parts-list-cb550
Just compare the engine- and framenumbers of yours with those listed in the first 4 pages to determine what goes for your model.
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Talking cutaways, what does this 2.5 refer to?
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The cutaway is the curve cut into the bottom of the slide. 2.5 means the cutaway is 2.5mm deep at its' deepest. The less cutaway, the richer will be the mixture at off-idle openings.
I went from 2.5 to 2.2 as an experiment only to find negligible difference. Goes instantly weak off idle. I'm more used to Amals and SU's and they never do that, however bad they're set up. All very odd.
I expect I'm missing something totally obvious, but what ?
Carbs off again today while the sun's hot on the rubbers.
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Deltarider, thanks for the 2 references above. It confirms the slides are 2.5. One thing I noticed is a reference to a slow jet. There is'nt one on the parts diagram so presume it's a drilling. Must check that for size.
Carbs are now off (again ).
Have to be really thorough this time, especially the needles.
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Could an overview be useful?
The original intake system on these it would be easy to describe as exquisitely resolved, for a 1970s engine with such smooth idle, linear response all the way to 10,000rpm without glitches and roughly 100bhp per litre, they deserve that wording as such a finely designed and specified production ready engine.
They are veeeery sensitive to any changes in their components though, that's either the vacuum characteristics, fuel levels or ultimately jetting.
There's effectively no facility to competently alter the vacuum curve, with any shifts in carburettor feed likely to need out of range jetting compensation to get toward where Honda set them. Even the airbox lid in different specifications will shift the balance.
As you note from experience with Amal and SU (I alter vacuum gradient on SU with oil viscosity to trim above and below target for transient openings) that tool is missing here.
The compression and cylinder draw on this engine is a serious consideration as they will run quite well with very significant upper cylinder damage, but with some odd response effects. This thread http://www.sohc.co.uk/index.php/topic,14049.0.html may give some idea if you look through at the state of the pistons when dismantled.
As already mentioned by others, current pattern brass components are often no match at all for the accuracy of the original parts. Kiehin where particularly good in production parts.
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One thing I noticed is a reference to a slow jet. There is'nt one on the parts diagram so presume it's a drilling. Must check that for size.
It should be in the parts diagram, part 17 in: https://www.cmsnl.com/honda-cb550f2-super-sport-550-four-1977-england_model17121/partslist/E17-1.html
Anyway, it's supposed to be a #38
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The reference I saw was to a slow jet, but not stated as idle jet. I assumed it was meant to be slow air jet, I've seen them quoted as 150 and 220. 220 could be for the 750's though.
No problem with the idle jets, original 38's, the long ones you illustrated . They do seem to be nearer 40 though but it idles OK at the right air screw turns out.
I checked the air entry hole which is in the air box side of the carb mouth. I assume that is what is referred to as the slow air jet. It works out as a 180, much more air than a 150.
The original needles are now back in. The difference in diameter at set points amounted to nearly 2 needle clip positions weaker.
The new main jets with their O rings are a firm push fit, but just in case, I shall get "proper" O rings on Monday before re-fitting the carbs. Will put the ignition back too so it's a fair comparison.
Here's hoping.
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Just found the reference to a slow air jet - it's in an addendum to the CB550K manual, shows a fuel level of 14.5mm so must be a different version of these carbs.
If anyone's got some 069a's accessible and can measure that small air drilling to the side of the venturi, that would be a
very useful bit of info. My guess is 1.5mm, but confirmation very welcome.
Anyone ?
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Just found the reference to a slow air jet - it's in an addendum to the CB550K manual, shows a fuel level of 14.5mm so must be a different version of these carbs.
That concerns the later K3 and K4 models which had totally diferent PD carbs. See pic below. Just to make sure: what type do yours have: the PD or the oldstyle?
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That's helpful, mine are the ones in the lower photo. Don't know what model ref . It would be great to check the size of that air drilling in the carb face before the carbs go back on again. probably correct, but worth checking if they are part of that massive weakness bottom end.
The way it went more and more rich when well up the rev range is strange, especially with that thin foam filter in. That would normally weaken it off . I have read on here that it could be fuel being pulled past inadequate O rings on the main jets. They are new on the aftermarket jets, I will get some better ones tomorrow even though they are are a reasonably firm push fit.
The jets do check out as 98 though.
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After being side-tracked by other things, finally had another run with the original needles back in. That's all the original internals now back in, clip 2, float levels correct. Ignition back to standard. Screws 1.1/2 out.
Started fine , sounded good, had to take the choke off very early (opposite to before) as it was showing very rich on the Lambda reader. Even after 10 miles it was showing way over rich the full range of throttle and yet STILL had a small stumble just after opening up.
Back home, took the plugs out, jet black.
All I've done is put the original needles back in !
The aftermarket needles had made it vastly weak right to the middle range , then too rich top end.
I tried some new main jet O rings, 1.2x4 (on stock, 20p for 4 ), but I'm waiting for some 1.2x4.3 which calculate as the right size (80p for 4 ). Maybe that's the top end richness issue, can but try........
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Interesting there's so much difference and echoes that which most find, that current replacement are highly suspect.
Be interesting with the replacement O-rings to see if it clears out the top end jetting.
Have you got paper filter in yet? as I'd perceive that to make difference to that just off idle characteristics of slightly lean. If it's with a new filter, then it looks like perhaps 1/4 turn in on airscrew would assist.
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1.2x4 should do, as the originals AND the new aftermarkets were 1x4. But, the stretch on 4 may be just a little too much and not enough crush. Cheap enough to try some 1.2x4.2.
I've tried it with and without an air filter, both paper and the foam that was in it. No difference. All I can do is try something else and see what happens. The difference on needles is incredible. I'm going to try the aftermarkets, which made it too weak bottom end, but in one clip richer. At least with the Lambda in I can see the results clearly and it stops me making wrong assumptions.
These carbs seem very sensitive to small changes, I suppose that's a product of a small choke size.
I know it's said these carbs need the original brass bits in, but I suspect there is wear in the needle jet, that would explain the issue somewhat, not entirely sure what size it should be, more research req'd. Must find Deltariders chart again.
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"These carbs seem very sensitive to small changes, I suppose that's a product of a small choke size."
Looking at it logically, creating the carburettor bore size for maximum rpm of each cylinder and aiming for an ideal airspeed at that point will give a proscribed venturi size they felt was optimum.
Going to the other end of the range, at idle, then some very small metering is required to get a linear hiccup free response. Quite a balancing act, along with tiny changes shifting the AFR in fairly large percentage terms.
Always learn more about something when it's not working properly though as it makes us think harder.
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The compressions have been mentioned on here, finally got 'round to a check :
cold engine, 150 psi on all 4, give or take 1 psi. Looks OK to me for a mere 9 to 1 engine.
Hopefully the 1.2x4.2 O rings will turn up today and I can put the carbs back on and try the latest changes and adjustments. Trial and error. I think I now know what was going on, soon find out !
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Compression looks pretty decent, interesting to hear what you get when you feel you've all the obvious bugs out of it.
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The new aftermarket needles back in, 1 clip richer as previous runs showed the new needles made it way too weak .( much fatter profile than the originals). It's clear to me that the needle jet is worn ( it's done nearly 67,000 miles ).
Incredibly, the Lambda reader showed over-rich the entire range, right up to 70mph. I took the air filter out at the roadside, no difference, just lots of extra noise .
After suggestions on here, I had set the air screws slightly on the rich side to partly improve the pick-up off idle. Still ticked over OK.
As an experiment, I turned the screws out to 1.1/2 and had another run. All the richness gone, right up to 65 70mph. The idle system was feeding the whole carb range, BIG style. That's a new one on me, I've had this Lambda set-up in my Austin Gipsy (Zenith), my Citroen DS (twin choke weber) my Triumph T100 unit twin (Amal concentric ) and my Cortina estate (Ford/Weber), none of them had the idle system working the whole range. Only the bottom end.
The idle jets are stamped 38 but measure 41, next step , change the idle jets, but , for now, it's running the best so far.
Glory be.....
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Just seen this that shows jet range - may help?
https://www.caferacer.net/threads/cb500-four-4-to-1-exhaust-dilema.23465/page-3#lg=thread-23465&slide=0
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Thanks Phil, I had spotted that chart a week or so ago. Quite different to some I have seen, much bigger overlaps. The idle system on mine is'nt just an overlap, it's a whole range mixture feed ! Without putting the Lambda reader in I would not have seen that. I suspect that the bigger size of the idle jet in it is possibly allowing too much volume into the choke area. I'm waiting for some 35 pilots to try as a test.
I had spotted something else somewhere regarding Keihin type 1's, an article describing how someone had worked out that going to a smaller idle jet helped the transition off idle. I wish I could find it again. That's what I will be trying next,
although to be fair , she's running really well now with the changes I've made, clean acceleration all the way except the slightest stumble just off idle, good tickover. Good plug colour.
All this effort has turned a very badly neglected bike into a pleasant ride.
I've learned a lot about CB550f's too !
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Further to my earlier post re a theory I read about smaller idle jets curing a bottom end stumble :
Finally got around to fitting the smaller idle jets. The originals checked out as 41 and it idled well on them with the air screws 1.1/2 out.
The new ones are stamped 36 and checked as 36. Had a run this afternoon and it idles well (again at 1.1/2 out ) and carburates clean the whole range. No off idle stumble and even pulls clean from low revs in a high gear.
In short, it runs perfect.
It seems illogical, but it works, it's now a pleasure to ride.
Less is more !