Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Beefington1975 on September 19, 2022, 02:12:41 PM
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Hello all,
I've used some of the excellent advice here to help me get my 500 k1 on the road. It was fine for a while, but has developed a running issue. I'm hoping for some thoughts/help on why it does what it does, please.
The bike will start, but will often cut out when pulling off. Then, after a short period of running it will fade at low speeds (making turns etc). The bike then won't start easily. And (strangely) seems more likely to start when on the side stand. When it does start again, only high revving will keep it going. I then have to nurse it back home, cutting out regularly trying to restart it.
So far, I have:
Cleaned and repaired the carbs
Fitted R9 fuel lines and fuel filters
Changed the spark plugs and caps
Adjusted the valve clearances
Synchronised the carbs
Checked the battery and charge (12.5v at idle, 13 5v at 4000 rpm). I did notice the voltage drop to 10v on start-up.
The bike has electronic ignition fitted- so no timing to adjust.
Can anyone offer some advice as to what to check next?
Many thanks
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Are you using the original coils ?
Are the leads still coming cleanly out the coils or has the outer lead started to separate worth a check.
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What make of ignition?
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Are you using the original coils ?
Are the leads still coming cleanly out the coils or has the outer lead started to separate worth a check.
Thanks for the response.
The coils look to have been replaced by the previous owner fairly recently. The leads look clean and solid as they some out of the coils.
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What make of ignition?
Thanks for the response. It was from David Silver Spares - fitted by the previous owner in 2016
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Fading at low speeds sounds like a fuel issue.
Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?
Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.
Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.
Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.
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Fading at low speeds sounds like a fuel issue.
Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?
Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.
Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.
Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.
Thanks for responding.
I thought fuel at first, so took the carbs off and on again, stripped and cleaned them and checked the rubbers and clamps - all look in good condition. Will try carb cleaner as you suggest.
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Fading at low speeds sounds like a fuel issue.
Have you checked the vac gauge adapter screws are secure and fitted with an alloy washer?
Have you checked the inlet manifold rubbers for cracks. I suspect an air leak somewhere, enough for it to overwhelm the mixture at low speeds and why high throttle openings still work, as it would on choke.
Also check the manifold clamps, possible a screw has failed allowing the clamp to become loose.
Try the carb cleaner trick, start the bike and spray carb cleaner around the inlet side and see if the revs increase, if they do, you have a leak.
Thanks for responding.
I thought fuel at first, so took the carbs off and on again, stripped and cleaned them and checked the rubbers and clamps - all look in good condition. Will try carb cleaner as you suggest.
Tried the carb cleaner trick - didn't change the idle speed.
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Inline fuel filters are a no no. Please read:
http://forums.sohc4.net/index.php/topic,190857.msg2220841.html#msg2220841
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Inline fuel filters are a no no. Please read:
http://forums.sohc4.net/index.php/topic,190857.msg2220841.html#msg2220841
Thank you. I'll take them off, but only added them after this issue developed in the hope it would help. I wondered if it sediment was blocking the idle circuits
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As a test you can turn the air adjustment screw inward until they are 1/4 out from closed to see if it then runs rich (more like on choke) and assess if the idle circuits are flowing any fuel.
Just a way of seeing if there's any response there not to set them longer term.
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From original description, running on wider throttle and not lowered throttle openings, it does suggest there's some impairment of the idle fuelling circuit though.
If you can get them out in situ, it could be worthwhile checking the idle mixture jets to see if they are clear.
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Anything that passes the petcock filter is fine for the carbs. Slow jets are known to become partially blocked when bike is not used for a long period of time. Good fuels like V-Power and Ultimate can help. An additive, a socalled fuel system cleaner, can also help as long as there's still some opening. To have a first impression of the condition of the slow jets, have the bike idle and turn the airscrews completely in and then three turns out to detect any change in RPM. This is done one after the other and wait a few seconds after you have turned the screw. RPM will not change much but if it doesn't change at all, it's an indication that that particular idle circuit is not functioning as it should. Then it's time to remove the slow jet for inspection. This can be done with the carbs remaining on the bike. Removal of the floatchambers will make all 4 accessible for removal and cleaning. Please report back when you intend to do this for added advice. Blocked or partially blocked slow jets is a common issue.
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Anything that passes the petcock filter is fine for the carbs. Slow jets are known to become partially blocked when bike is not used for a long period of time. Good fuels like V-Power and Ultimate can help. An additive, a socalled fuel system cleaner, can also help as long as there's still some opening. To have a first impression of the condition of the slow jets, have the bike idle and turn the airscrews completely in and then three turns out to detect any change in RPM. This is done one after the other and wait a few seconds after you have turned the screw. RPM will not change much but if it doesn't change at all, it's an indication that that particular idle circuit is not functioning as it should. Then it's time to remove the slow jet for inspection. This can be done with the carbs remaining on the bike. Removal of the floatchambers will make all 4 accessible for removal and cleaning. Please report back when you intend to do this for added advice. Blocked or partially blocked slow jets is a common issue.
Many thanks for the detailed advice. I shall try the air screw test. I have already cleaned out the pilot circuit on each carb (using a very handy guide elsewhere on this forum). This was making me hope it wasn't an ideal circuit issue - all channels were clear. I can't see how to remove the pilot jets with the carbs in situ so am hoping pulling the carbs again will be a last resort!
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Thanks to all that have advised so far.
I've adjusted the air screws as suggested (to check the ideal circuit) and the revs change in the same manner as I adjust each cylinder. This indicates the ideal circuits are clear (?) - I admit to some wishful thinking here as, having pulled the carbs and cleaned them/checked for flow, I am loathe to pull them again so soon! Will do so if that's where the advice takes me though, of course.
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I’d say the idle circuits are clear.
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I’d say the idle circuits are clear.
Does seem positive from that report.
Beefington, have you tried setting the idle circuit as per Honda manual to optimise the carbs as they stand now?
It involves warmed engine, then winding outward individually ( successive carbs) until the rpm reaches a peak with that cylinder, then just as it starts to falter from mixture going too lean, turn it back inward to drop the rpm by 100. Then reset overall tickover speed with main control and move to next carb. Complete all four and that should be a reference setting for your engine equipped with those carbs and jets. This routine should establish if the very slow running is able to work correctly.
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I’d say the idle circuits are clear.
Does seem positive from that report.
Beefington, have you tried setting the idle circuit as per Honda manual to optimise the carbs as they stand now?
It involves warmed engine, then winding outward individually ( successive carbs) until the rpm reaches a peak with that cylinder, then just as it starts to falter from mixture going too lean, turn it back inward to drop the rpm by 100. Then reset overall tickover speed with main control and move to next carb. Complete all four and that should be a reference setting for your engine equipped with those carbs and jets. This routine should establish if the very slow running is able to work correctly.
I haven't tried that. Will do tomorrow and report back. Thank you
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My latest fiddlings suggest that the bike is running too rich a mixture at idle - brand new plugs covered in soot after just a few minutes of running. Is this the root cause? Or a symptom?
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I'm no expert - far from it - I would judge how rich or lean an engine is running after say a ten mile ride - when engine has cooled check the plug colours.
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If started on choke they'll be fairly black, should get lighter after some running if it's ok.
Basics though, choke open and close fully without impairment? Air filter ok/clean/new ? Just to check the obvious.
Moving on, what do you have the idle adjustment mixture screws set to now ?
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I'm no expert - far from it - I would judge how rich or lean an engine is running after say a ten mile ride - when engine has cooled check the plug colours.
I wish it would run long enough to ride 10 miles!
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If started on choke they'll be fairly black, should get lighter after some running if it's ok.
Basics though, choke open and close fully without impairment? Air filter ok/clean/new ? Just to check the obvious.
Moving on, what do you have the idle adjustment mixture screws set to now ?
Hi. I didn't need to use the choke to start the bike. Ran the bike long enough to perform the check you described. Have to be honest and say that the changes in rpm were very slight so not sure I got the screws spot on. The are set to about 1.5 turns out.
The air filter isn't new, but looks good (not that old). The choke opens and closes easily and fully
Many thanks
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Try with the screws set at 2 1/2 turns out and see if that gives anything in the way of sensible running, or improvement at all.
It does appear to be too rich.
Do you know which size of idle jet is fitted to them ?
More rudimentary check is to remove air filter and see if that improves running.
Really just trying to get further assessment to help indicate what may be out of kilter.
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Try with the screws set at 2 1/2 turns out and see if that gives anything in the way of sensible running, or improvement at all.
It does appear to be too rich.
Do you know which size of idle jet is fitted to them ?
More rudimentary check is to remove air filter and see if that improves running.
Really just trying to get further assessment to help indicate what may be out of kilter.
The idle jets are 40s. I'll try the aircrews at 2.5 turns out and take it for a spin (won't be able to do this for a couple of days though). Many thanks for the help so far.
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Must admit. Turning the air screws on mine makes little if any difference to the engine rpm.
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Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???
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What exactly is sooted? The thread's end? That's normal. Focus on the plugs nose, the ceramic insulator that is. Realise the CB500s plugs soot very easy at idle. Back then we used to ride these bikes. Nowadays and in this forum in particular, more and more owners seem interested in having a perfect idle they can listen to sitting in a deckchair. ;)
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Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???
I would only expect a high oil level to become an issue at high engine rpm due to excessive oil misting
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What exactly is sooted? The thread's end? That's normal. Focus on the plugs nose, the ceramic insulator that is. Realise the CB500s plugs soot very easy at idle. Back then we used to ride these bikes. Nowadays and in this forum in particular, more and more owners seem interested in having a perfect idle they can listen to sitting in a deckchair. ;)
Both the centre and end electrodes are sooted. Listening to it from a deck chair is not my aim...but it is all that's possible at the moment. It won't even make the move from 0 to 2 mph without cutting out.
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Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???
I would only expect a high oil level to become an issue at high engine rpm due to excessive oil misting
OK. Thank you. I'm grasping at straws I think
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Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???
As Ted indicated, I stood don't feel there is any effects likely from this. They have more tolerance to raised oil level that this amount.
Wouldn't discount the air filter as suspect though. Any significant impairment with this will impact that mixture and not be readily evident from just looking at the filter. Definitely worth trying with it removed to at least give you a check on condition and flow impact to running. Easy and costs nothing too.
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Just a thought...saw someone on another thread suggest that engine oil level could be a factor? I've checked mine and it's on the top line. The deposits on the plugs look dry, but could the fouling be due to excess oil???
As Ted indicated, I stood don't feel there is any effects likely from this. They have more tolerance to raised oil level that this amount.
Wouldn't discount the air filter as suspect though. Any significant impairment with this will impact that mixture and not be readily evident from just looking at the filter. Definitely worth trying with it removed to at least give you a check on condition and flow impact to running. Easy and costs nothing too.
Ok. Thank you. Will try it with the air filter out 👍
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Try with the screws set at 2 1/2 turns out and see if that gives anything in the way of sensible running, or improvement at all.
It does appear to be too rich.
Do you know which size of idle jet is fitted to them ?
More rudimentary check is to remove air filter and see if that improves running.
Really just trying to get further assessment to help indicate what may be out of kilter.
Had some time to tinker today
I removed the in-line fuel filters and ensured the fuel lines were stock length.
I then wound the air-screws out to 2.5 turns and took the bike for spin.
It ran very well, a pleasant surprise. I covered about 10 miles - mostly low speed (30 - 40 mph) with a few bursts of speed (up to 60mph) . No poor running evident. Checked the spark plugs and they seem 'normal'/optimal
Not sure what this means - as it ran much better at a non-stock setting.
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For some reason it seems to be getting just a little excess fuel at the very low end of carb range.
Setting the screws out further will not change the metered fuel from idle jets at their maximum (roughly half way through carb opening) as that's controlled by the 40 sized orifice. What the air modulation does is to change the "ramp" angle leading to that point by bleeding more air through than fuel at the very base of throttle slide opening.
Honda don't state an absolute for this setting of air jet, more a competent start point to be refined during setup. Obviously this case you can see the response from resetting them (indicating circuits are working reasonably) and ending up at 2.5 out is probably at the far end of range reality, but not unworkable. Probably more assessment is valid here to see if you've any unwanted complications and perhaps see if anything else is out of the ordinary over further mileage.
At least if it runs well you've got a chance to now get more comprehensive view.
The inline filters, I'd definitely not associate with low speed fuel demand and feel confident to discount those in this area of carburetor work. Usually it's peak flow that is of concern with these and inadequate supply volume to replenish float chambers fast enough when flat out and wide open throttle. The float chamber of course acts a constant reservoir to the jets and will ordinarily have no problems at low speed.
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For some reason it seems to be getting just a little excess fuel at the very low end of carb range.
Setting the screws out further will not change the metered fuel from idle jets at their maximum (roughly half way through carb opening) as that's controlled by the 40 sized orifice. What the air modulation does is to change the "ramp" angle leading to that point by bleeding more air through than fuel at the very base of throttle slide opening.
Honda don't state an absolute for this setting of air jet, more a competent start point to be refined during setup. Obviously this case you can see the response from resetting them (indicating circuits are working reasonably) and ending up at 2.5 out is probably at the far end of range reality, but not unworkable. Probably more assessment is valid here to see if you've any unwanted complications and perhaps see if anything else is out of the ordinary over further mileage.
At least if it runs well you've got a chance to now get more comprehensive view.
The inline filters, I'd definitely not associate with low speed fuel demand and feel confident to discount those in this area of carburetor work. Usually it's peak flow that is of concern with these and inadequate supply volume to replenish float chambers fast enough when flat out and wide open throttle. The float chamber of course acts a constant reservoir to the jets and will ordinarily have no problems at low speed.
That makes sense. I'll run it as-is for a while and keep monitoring. Will change the air filter too to rule that out as a factor.
Thank you for the generous help and information - it's paying off and I've learned a lot.
Cheers
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The last few of posts got me tinkering with my 500 K1 as it's raining. I have been unable to get it to idle at low speed it just cuts out or runs at over 2k rpm - let off the main stop screw just a fraction and it stops.
I've not done anything to the carbs as I was not too bothered about how it runs as long as I can try out all the gears on a short run.
So I checked the four air screws - they were all set at around 1.5 turns. I moved them to 2 turns then fired her up and let off the throttle stop screw a tad again - she now idles quite comfortably at around 1200 rpm. Yes not perfectly even yet but so much better than it was - gives me more confidence that it will not conk out on a run now.
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For some reason it seems to be getting just a little excess fuel at the very low end of carb range.
Setting the screws out further will not change the metered fuel from idle jets at their maximum (roughly half way through carb opening) as that's controlled by the 40 sized orifice. What the air modulation does is to change the "ramp" angle leading to that point by bleeding more air through than fuel at the very base of throttle slide opening.
Honda don't state an absolute for this setting of air jet, more a competent start point to be refined during setup. Obviously this case you can see the response from resetting them (indicating circuits are working reasonably) and ending up at 2.5 out is probably at the far end of range reality, but not unworkable. Probably more assessment is valid here to see if you've any unwanted complications and perhaps see if anything else is out of the ordinary over further mileage.
At least if it runs well you've got a chance to now get more comprehensive view.
The inline filters, I'd definitely not associate with low speed fuel demand and feel confident to discount those in this area of carburetor work. Usually it's peak flow that is of concern with these and inadequate supply volume to replenish float chambers fast enough when flat out and wide open throttle. The float chamber of course acts a constant reservoir to the jets and will ordinarily have no problems at low speed.
That makes sense. I'll run it as-is for a while and keep monitoring. Will change the air filter too to rule that out as a factor.
Thank you for the generous help and information - it's paying off and I've learned a lot.
Cheers
Takes a little time back and forth to work through things, but beneficial in giving you a clearer picture. At least it appears now workable and you get to enjoy riding it too, so all good.
Hopefully it will stay stable but you may need to consider again if air filter proves to flow a little more easily.
Let us know how you get on.
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The last few of posts got me tinkering with my 500 K1 as it's raining. I have been unable to get it to idle at low speed it just cuts out or runs at over 2k rpm - let off the main stop screw just a fraction and it stops.
I've not done anything to the carbs as I was not too bothered about how it runs as long as I can try out all the gears on a short run.
So I checked the four air screws - they were all set at around 1.5 turns. I moved them to 2 turns then fired her up and let off the throttle stop screw a tad again - she now idles quite comfortably at around 1200 rpm. Yes not perfectly even yet but so much better than it was - gives me more confidence that it will not conk out on a run now.
Yes Ted, it's a valuable tool to trim slow speed running. So often the manual specification is referred to as an absolute which I don't feel is what Honda meant it to be. These carbs are very accurate/repeatable/concise but with other elements affecting the critical metering of fuel in such small quantities, then valid adjustment is entirely practical.
Their method (Honda manual script) is a very benign but far reaching routine that's often missed when considering setup. In effect, it takes account of, successively;- fuel specification, air flow, valve efficiency in sealing, piston rings, dynamic compression, ignition performance, air density, barometric pressure (height above sea level) to fine trim the the slow speed running.
It is exactly what fuel injection system accomplishes with use of Oxygen sensors reporting from exhaust to trim the mixture for prevailing mechanical and atmospheric conditions. Not in such a repeating timeline, but the same process but using you as it's view of how it's running.
Turning airscrew out (not pd carb, they're opposite usually) brings the mixture toward to lean at probably 14:1 ish when it will start to miss partially, then back in to richen slightly (rpm drop by approx 100) to probably end around 12.7/13.0 to 1 at which point it idles well.
Fuel injection does exactly thus, with short duration trim values to cope with immediately occurring emmisions, then aggregated into "long term trim values" that the ECU keeps updated to maintain overall mixture given the equipment it's working with. If the long term trim values reach certain threshold then the ECU will throw a code giving "emmisions" warning, or needing workshop attention.
Our emmisions code for these would be roughly 1/2 to 3 turns out for nominally general operating conditions. Outside those we would consider then to exhamine components to find cause.
Dammed clever those Kiehin designers :)
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An update.
I had a very satisfying run out today. The bike performed well, no sign of the previous problems. If anything, I'd say the engine feels more responsive and 'free running'.
Covered about 40 miles this time. Checking the plugs at the end shows a little soot on the end of the threads and the bottom electrode, but the centre electrode and ceramic look ok.
Very pleased to have been able to enjoy a ride without trouble!
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Have the fuellines as close to original as possible and use that clamp! Realise there's not that much column to speak of and flow is impeded easily. Therefor: no extra filters!
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As long as the tank filter is intact everyone says that's enough.
On my 400 there was loads of space to fit a loop round the tool tray. My 500 has no space so I will have to remove the tap & check it is good - the one on my 400 was full of holes!
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My petcock - the later model without the bowl and the nylon filter protruding into the tank - is still the original. I've bought a spare seal though that goes between the tank mount and the petcock in case I might need it. Oh, you will not find it if you consult the fiches, but I got the part number by chance as it also used on some Honda outboards and CMSNL has it separate for € 4,-: https://www.cmsnl.com/products/o-ring118x355_16997467000/.
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Delta, this O ring is to seal what?
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Sorry for explaining it poorly, it's the big one here: https://www.cmsnl.com/honda-cb500k2-general-export_model50441/strainer-set_16952341671/
By buying the seal separately, I didn't have to buy that complete strainer set. Last time I had mine off, the seal looked aged. That's why I ordered a spare one.
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Teds 500 won't have that seal DR, it's the bowl type.
He will have an oring between the petrol tap and the tank but it's a thin one in an oval shape. Also one between the bowl and the tap.
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Both my replies #40 and #42 specified it well, Oddjob. Erny's CB550K1 has the same petcock mine has: https://www.cmsnl.com/honda-cb550-k1-four-1975-usa_model466/cockfuel-cb550f_16950374671/