Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: jon stead on April 24, 2015, 08:32:07 PM
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Hi
When I bought my bike teh carbs were flooding. I sent the carbs off for professional overhaul. They were set up on the bench. I got the bike running only to find oil leaks that weren't evident when it was stopped. The bike has been away and had the leaks fixed but the lad doing it couldn't get the engine to run correctly. Below are some of the comments from the emails he was sending me:
"Engine running no leaks. All the electrics are good with no issues. However, the engine hunts badly, revs to 3k when warm and when I adjust the throttle stop to set a tick over the engine dies. It won't idle at all unless I hold it on the throttle but if bring the throttle stop up to hold the throttle the rev climb to 3k again.
Ignition is spot on at static and full advance.
When I started the bike before I started work it did similar and commented that the carbs were miles out. Anyway I have removed and stripped and balanced the throttles, all of the floats are set to the same height, and all of the jets are (were) all matching across the carbs and the throttle slides are matching too. Need to do some research on these carbs are they correct for year etc.
For your records
slow running jet = 40
main jet = 100
Float height 23mm (should be 22mm but the springs in the float needles are very weak, they should hold the float a little but do not so 22mm turns into more like 20mm in use).
Air jets turned out 1 1/2 turns.
NEVER LEAVE THE FUEL ON, the float valves fitted are brass type not Viton tipped so they will pass a little fuel over time and eventually will overflow. As the bike is used the valves will seat a little better.
It runs horrible, those carbs are not at all nice. Both 1 and 2 flood intermittently, the whole bank is rich and doesn't want to idle at all again. I will have a go later.
I have worked on just about every type of carb but these things are doing my head in. The float needles will not seal, the needle springs have various tensions and the carbs slowly flood. I had them in a bath, they have been blown through, I have adjust the floats between 22 and 25mm height and the running is no better. I have altered the emulsion tube needles to run at 4 standard, 3 and 2. And the air screws have been everywhere from 1 to 2.5 turns out in 1/8 th turn stages. Again no better.
When cold the bike tries to run ok but when hot it doesn't want to know which screams "rich mixtures". The bike won't idle but I can hold it on the throttle at say 1500rpm but if I bring the throttle stop screw up and let this hold the throttle then the engine speed rises and hunts between 2500 and 3000 rpm, if I back off the throttle stop the engine does. I have had the carbs on and off, stripped and put back together more times than can remember. All the jets are correct size assuming the numbers stamped are a true reflection. I have even fitted a harder platinum evx plug set. "
I am now at a loss as to whether the problem is with teh carbs or somewhere else. How can I tell if the carbs are "worn out"? Any advice gratefully accepted.
Thanks in advance.
Chris
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Hi Chris, I feel your pain, after 7 months in storage i got my 500 out today and i am having the same problems even after it was running spot on when it went in to storage. I will have a look tomorrow to see what i can find. I will start with the carbs as they are flooding after a while and it is sitting at 2500 rpm and will not drop.
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I swear the bloody fuel in the Uk is getting worse and worse. Somehow I think the ethanol (in addition to knackering the rubber components) affects the float valves on our vintage carbs...
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mine has become more sensitive to slow running and temp,at present it runs at about 1,100 rpm quite well,
same jets as stated,BUT the air screws are only 1 turn out,the extra 1/2 turn does upset the slow running,
also check plug gaps,no more than 27 thou,
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Had similar issues when I laid the bike up a few years ago, but with 550k3 carbs fitted. I am reverting to original ones for the rebuild, really hope I don't get this. Redex is worth a shot, might have additives that help the petrol behave better from some reafing I have done on other forums. I did find my rebel 125 started behaving a bit like this on Tesco fuel, ran the tank near empty and filled up at tesco, bike was running badly until run near empty again, filled up at my regular Texaco stop, bike returned to good form, only problem in the list I didn't get wss overflowing carb on the rebel. Makes fuel quality a possibility to try, just in case.
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I stay well away from any ethanol petrol its shite and absolutley NO GOOD for our classics.
Cheers
Bitsa
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If your carbs are flooding you have no chance of getting it to run correctly. Check the brass tube in the float chamber. They are prone to cracking, then they will flood whatever the float valve is doing. I had this problem and cured it with a thin smear of epoxy resin adhesive.
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New float needles and seats are worth fitting if the tiny springs are week
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I swear the bloody fuel in the Uk is getting worse and worse. Somehow I think the ethanol (in addition to knackering the rubber components) affects the float valves on our vintage carbs...
This is quite interesting info regarding ethanol in petrol.
http://www.groups.tr-register.co.uk/wessex/ethanol-update.html
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Thanks everybody for the responses and some good tips there to be getting on with. Much appreciated. I will let you all know how I get on. :)
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Long shot, I know, but are there any other carbs available that would fit? MOre modern and more relaible ones?
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If fixed they are perfectly reliable. Got 180,000 + out of my originals with no more work than the odd redex treatement if thd carbs started leaking, which was not that often, and genrally only when the fuel tap was left on when standing, only had it overflow when on the move a few times, redex in the fuel for a tankfull and running the last half mile with the fuel off always cured mine, for at least the next year. They genrally only gave issues if the bike was stood for a few weeks or more, used daily they were better, my 550k3 carbs gave better economy but more issues.
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New float needles and seats are worth fitting if the tiny springs are week
I am going with Bryan on this one and will fit a new carb kit. Worked before on a 550F.
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If fixed they are perfectly reliable. Got 180,000 + out of my originals with no more work than the odd redex treatement if thd carbs started leaking, which was not that often, and genrally only when the fuel tap was left on when standing, only had it overflow when on the move a few times, redex in the fuel for a tankfull and running the last half mile with the fuel off always cured mine, for at least the next year. They genrally only gave issues if the bike was stood for a few weeks or more, used daily they were better, my 550k3 carbs gave better economy but more issues.
Matthew, that's answered my next question then, "Would I be better off with a set of 550 carbs on it?". I guess not from your experience.
The switching fuel off before you get home I've heard of before, never put it into practice, but I can see the merit in it. Just got to persevere with these ones then :-(
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I am not at all sure about if the 550f carbs would be any better, the k3 ones are leaner jetted and rather different I think. I never had a 550f bike to know the differences. Does sound like the new needles and float seats will be a good next step. Deffinately helped on a 6 foot cut knife mower I helped my dad fix recently, though due to it's total obscureity the options open to us were brand new carb from bing direct for £400 or search ebay for anything used, which eventually paid off after over a year of searching ebay.
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is this kit any good,
needle,jets ,"O" rings,etc,
all for under £20 + p&p + VAT
http://www.davidsilverspares.co.uk/CB500K1-FOUR-1972/part_61450/
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is this kit any good,
needle,jets ,"O" rings,etc,
all for under £20 + p&p + VAT
http://www.davidsilverspares.co.uk/CB500K1-FOUR-1972/part_61450/
That works out, all for under £100 John. These are cheaper >> http://www.ebay.co.uk/itm/161492636759?_trksid=p2057872.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT
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is this kit any good,
needle,jets ,"O" rings,etc,
all for under £20 + p&p + VAT
http://www.davidsilverspares.co.uk/CB500K1-FOUR-1972/part_61450/
That works out, all for under £100 John. These are cheaper >> http://www.ebay.co.uk/itm/161492636759?_trksid=p2057872.m2749.l2648&ssPageName=STRK%3AMEBIDX%3AIT
thanks Trigger,at present mine are behaving (fingers crossed) but will try to remember for the future,I wonder if the Thread starter ; Jon Stead,will find it interesting?
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He said that he had the carbs done John but, i am wondering if they just cleaned the internals ?
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^^ Hi lads, yes saw your posts about spares kits. When teh carbs were rebuilt it was all new David Silver parts inside. The carbs are going back to the overhauler when I get home for him to have another look at now that there are some known faults and feedback. Hopefully he can make them work.
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recently I have noticed the carb setting are more critical,
years ago,it would run with the airscrews open 2 turns,
now ,it is only 1 turn,and 1/8 either way makes a difference,also,what is the state of the air filter ??
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Also worth checking for any burrs / unrefined castings on the float pin struts - just a bit of fine wet / dry to clean them up can often make the difference.
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Thanks for all the tips, much appreciated
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fitted a whole new carb kit and still have the same problem as Jon Stead. Rev's drop after a while but, as soon as you rev up it will not drop lower than 3,000 rpm. Another head scratcher and not sure which way to go.
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Try removing the cables Graham and blipping the throttle by using your hand on the butterfly. If it doesn't do it, then the problems the way the cables are routed or the way they are connected, sometimes easy not to leave enough slack in the cable or the cables sticking.
Cheers Oddjob. Already gone down that route ;) Even put a electronic Vacuum mate on the carbs so, the balance is perfect.
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You checked the throttle stop screw on the butterfly? it's an eccentric cam arrangement and if it's out it will hold the throttle open even with no cables attached.
Will go through it again tomorrow. I can get it to tick over at 800 rpm but, twist the throttle to 7,000 rpm and it will only return to 3,000 rpm and after a while will return to 800 rpm or drop off completely.
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Possible air leaks between carbs and head? O-rings between head and intake manifold are always suspect.
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^^^thanks Delt Rider.
Got the bike running today but it will not tick over. Rides ok ish, apart from a horrendous front wheel wobble and once warmed up is a pig to restart.
When I get more time I will check for air leaks as suggested. At the moment I'm just glad I actually got a rude out if it. Gears work, brakes work, no engine oil leaks, so just this wheel wobble and tick over and jobs a good'un.
Thanks everybody for your support and suggestions, much appreciated.
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Have you checked the idle jets/emulsion tubes?
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Outside chance here, but the bit about being a pig to restart once hot reminded me of my first cb550, it had most of the same symptoms as I recall, it was down on compression thanks to the rings being mia on top of pistons.... If you don't know the history of the inside of the engine, it might be worth just checking compression. Mine still pulled a ton with the engine like that, pretty well inpossible to start once hot, tickover a pain to get anywhere near right. Valve clearences were often needing adjustment too. Worth a quick check in my books.
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^^^ Thanks Matthewhouse. Compression has been checked and confirmed good, but I agree it could of been the cause.
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Hello all, my poor running engine saga continues. Because I work away a lot I don't get much time to work on it. Since last posting, the head has been off, cylinders rebored, new pistons and rings fitted. The carbs have been back once more to the original overhauler but still the same symptoms. Won't tick over and runs hot so must be rich. I will pass the suggestions from this thread to the guy that's got my bike now. I'm close to deciding to bin these carbs, despite the amount of money spent on spares for them, and getting another set. It would be great if I had a set if carbs that I know work correctly so I could try them and know for sure.
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Hello All. Changed the old carbs for a newly refurbished set from the USA. Bike is running as good as it's ever done whilst I've owned it. New swinging arm bushes fitted, new battery, new MOT and I've been out n it today. Taking it easy considering the rebore and hopeful of the bike improving all the time now.
Tickover still erratic, nice when first started, but rises the 2,500 rpm when warmed up. I can live with that. I think the tank is rusty and cruddy so next job is to clean the tank out with some drain cleaner and get some miles on the engine.
Typical that I get to this stage at the end of the summer!
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Hello once more. Yet again I am away for some months and have had to interrupt my bike's progress. Before I left though, I managed to clean the tank out and refilled with new fuel. I am struggling to get more than 6,000 rpm out of the engine. I'm thinking that the mixture is too rich and possibly needs more air. Also maybe some of the tank crap had got through to the carbs so I'll check the jets when I get home. SO frustrating not having the time to get to it. It's slowly getting better as I do more to it and I feel that it's something relatively simple now.
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check your plugs,running HOT tends to be to lean,
rich will mean sooty plugs,
how soft are the carb to head rubbers?as they age,they get hard and can leak air
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HI johnwebley, thanks for the reply. Since the second set of carbs the engine isn't running hot anymore and the plugs aren't sooty but the engine is down in power and won't rev over 6,000 rpm.
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What a momentous day, today, has been in the saga of my 500/4. I feel a huge corner has been turned, a momentous mile stone reached and many more similar metaphors you can think of.
The bad running of my bike continued, so bad it was unridable. I didn't have the time it needed to sort it properly, but whilst working away, I continued researching my symptoms, and found an article about powering the coils straight off the battery, bypassing the ignition switch and the cut off switch. I also downloaded a copy of the electronic ignition system that had been installed on the bike a few years ago, shortly after I'd bought it.
I set to this morning and made up my bypass lead. As I looked at the coils and the wiring diagram to work out where to connect to, I noticed that my coils were wired in parallel and they should be in series. I rewired them, as per the manufacturer of the electronic ignition systems diagram, and hey presto, a transformation occurred. The engine fires first time, every time on the button. The engine ticks over smoothly now and revs freely. I am over the moon.
It still needs some fine tuning but for the first time in three years I am out and about on it with a huge degree of enjoyment.
Thank you to all who have commented and offered advice along the way, much appreciated.
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Boyer ignition?
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What a momentous day, today, has been in the saga of my 500/4. I feel a huge corner has been turned, a momentous mile stone reached and many more similar metaphors you can think of.
The bad running of my bike continued, so bad it was unridable. I didn't have the time it needed to sort it properly, but whilst working away, I continued researching my symptoms, and found an article about powering the coils straight off the battery, bypassing the ignition switch and the cut off switch. I also downloaded a copy of the electronic ignition system that had been installed on the bike a few years ago, shortly after I'd bought it.
I set to this morning and made up my bypass lead. As I looked at the coils and the wiring diagram to work out where to connect to, I noticed that my coils were wired in parallel and they should be in series. I rewired them, as per the manufacturer of the electronic ignition systems diagram, and hey presto, a transformation occurred. The engine fires first time, every time on the button. The engine ticks over smoothly now and revs freely. I am over the moon.
It still needs some fine tuning but for the first time in three years I am out and about on it with a huge degree of enjoyment.
Thank you to all who have commented and offered advice along the way, much appreciated.
great news,and still lots of warm weather to enjoy it
now its running ,use it,they love being used
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Boyer ignition?
Yes, Boyer Brandon, Micro Power system.
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Nice one, well done Jon.
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One of the boyer ignitions uses standard coils the other uses 6 volt coils in series(or 3 x 4 volt if its a triumph trident)giving extra wasted sparks. Its over 35 years since i fitted one so cant remember which is which
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This Boyer system uses two, 12volt, coils in series. The difference was unbelievable once I'd rewired them from parallel to series.
This morning, I put the "old", albeit overhauled carbs back on, and it fired up and sat happily idling on the first touch of the starter.
Edit:
Just rereading above, I guess two 6volt coils in series would give 12volt total?