Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: Siloxious on November 02, 2023, 01:44:54 PM
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Hello everyone!
I had an awesome weekend, I was finally able to get my CB500 Four running! After a year and a half of work on the bike, it came to life. While wrestling with the ignition, I noticed that the previous owner had installed the cam of the ignition advance 180 degrees wrong. After fixing this, the engine came to life with only one kick with the kickstarter. Now, another chapter of the restoration begins!
The engine starts brilliantly, no problems with starting and runs on all four cylinders (the exhausts become hot). However, it cuts off when idling. When I use the throttle, the engine reacts. But beneath 2000 rpm, it begins to sputter and beneath 1000 rpm, it cuts off. It just doesn’t idle at all. I noticed that cylinders 2 and 3 are hotter than 1 and 4. Would anyone know what the problem could be?
The next thing on my list is doing a compression test of the cylinders as I’ve not gotten around to it yet. And if I can manage to get the engine to idle, I’d like to do a carburetor synchronisation.
Overall, it was a good weekend!
Cheers!
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Sounds like some of the idle jets or slow jets as they are sometimes called are blocked. Maybe some of the passageways that supply them with air as well. I presume you've tried using the thumb screw on the carbs to keep them going?
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Just so we're talking about the same screw: if you say thumb screw, do you mean screw number 42? I've put these in and gave them 1 and 1/8 turns from when they're seated all the way (as the shop manual mentions an air screw opening of 1 and +- 1/8).
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First things first. Compression test and synchronisation can wait.
For how long has bike been inactive and during that period, were the carbbowls empty or did they contain fuel? In case of the latter, inspection and cleaning of the slow jets is almost inevitable. On a CB500 you can leave the carbs where they are and just remove the floatbowls. Slow jets can then be removed by sliding a small screwdriver sideways into the slit to loosen them a bit. From there your fingers can unscrew them. Carb #1 can be a bit difficult because of the nearby clutch cable.
But I'd first begin with the ignition.
When you have the engine running, have a close look at the sparkplugcaps and see if you can detect any intermittent (!) arcing from the cap or its wire to the head. This is best seen in the dark.
Does the advancer move freely? Do you have a stoboscopic timinglight to verify a good functioning of the advancer and to check the timing?
The thumb screw is #58. You can reach it from the right side under the tank an adjust the general idle rpm with it.
#42 Are the airscrews. Don't touch them! At least not now!
#73 are the slow jets aka idle jets. They may need cleaning. May. First check and doublecheck the ignition.
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Thanks for the answer!
1) The bike (apparently) stood still for 2.5 years.
2) The carb bowls were dirty and there was a lot of gunk inside, so I would think they contained fuel.
3) I have already rebuilt the carbs by the instructions of Classic Octane a year ago. I've used a kit, so the jets are new. This is the video I followed: https://www.youtube.com/watch?v=JFTOfYl5BSc&ab_channel=ClassicOctane.
4) Half a year ago, I was ready to start the bike. I used a secondary fuel tank and no exhaust. I had a little accident with some leaked fuel :(. Nothing broke but I definitely learned that I should work safer. I then decided to first fully restore the fuel tank and fit the exhausts, so there would be a small chance of fuel leaking.
5) Now, with a clean fuel tank and exhausts, I started the bike again and it worked. Because I tried starting it half a year ago, some fuel ran through the carbs. So, it could be possible the jets are clogged. Would you suggest that I clean the bowls again?
6) The ignition advancer moves freely. When I noticed the cam was turned 180 degrees wrong, I decided to clean the advancer while I had to take it apart. I've lubricated it sufficiently.
7) Tomorrow, I can work on the bike. I'll check for that ark that you're talking about. I sadly don't have a stoboscopic timinglight, so I'll have to do with a static timing. I'll check the static timing tomorrow (I use a multimeter to test it, since I don't have a static timing light).
8) I've not touched the thumb screw in any way since I've bought the bike. So I guess I'll try it tomorrow.
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Get the original brass ultrasonic cleaned and refit as the kit parts are notorious for not being to Honda spec especially the needles and needle jets.
If it has points use a points file to clear oxidation and a SMALL amount of lube on the pivots
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[...]This is the video I followed: https://www.youtube.com/watch?v=JFTOfYl5BSc&ab_channel=ClassicOctane.
The best on the subject is Motormac. On Youtube: Motormac Honda CB500 four Vergaser. You don't have to see all of them. Language is German. But he's the best.
[...] Would you suggest that I clean the bowls again?
Personally I'd refit the original parts. Mine ran 140.000 km and still don't wear.
I've not touched the thumb screw in any way since I've bought the bike. So I guess I'll try it tomorrow.
That should be the first step. Who kniws? Aim at an idle of 1150-1200 rpm.
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The Honda recommended idle is 950-1050rpm for the 500, check the workshop manual if you are in doubt. If the engine is in fettle, as in good condition, it should quite happily tickover at that speed. Increasing the idle speed is like turning the radio up in a car to disguise engine noise. You really want to hear the noises, not mask them, if you can hear it you can work out wants wearing or what's going on inside the engine. An engine is top notch condition will tickover at less than 600rpm with little noise.
The thumb screw or number 58 lifts ALL the throttle slides on the carbs, if it's too low the engine will NOT tickover, almost an instant stall.
As Bryan says, put the original jets/needles etc back in, aftermarket jets are quite frankly awful, poorly made, lack of precision etc. Especially the float seat parts, they leak for fun as a rule.
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The Honda recommended idle is 950-1050rpm for the 500, check the workshop manual if you are in doubt. If the engine is in fettle, as in good condition, it should quite happily tickover at that speed. Increasing the idle speed is like turning the radio up in a car to disguise engine noise. You really want to hear the noises, not mask them, if you can hear it you can work out wants wearing or what's going on inside the engine. An engine is top notch condition will tickover at less than 600rpm with little noise.
Oddjob, with all due respect, what you suggest, is for much, much later.
Let's stay on the safe side and first have it idle at around 1100 rpm.
Oh and I'd welcome a video where a CB500 will tickover at less than 600 rpm. When I had everything top notch, I managed to get at an acceptable idle of 800 rpm. A Honda mec persuaded me to have it idle at around 1100 rpm. Allthough he didn't explain in depth, he said camshafts wear most at idle.
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Mine used to tickover quite easily at 600rpm DR, it would go as low as 400-500 before the engine started to knock a little, at no point did the oil light flicker.
Once it's rebuilt I'll gladly take another vid of the engine idling at very low speeds, it's just the sign of a really good engine IMO.
I'd agree, set a faster idle until it's actually running right, then lower it until it runs smoothly without too much noise.
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Looking fprward to it.
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I can get my 500 tickover down to 500 rpm - assuming the rev counter is accurate!
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Sounds like your engine is pretty well setup Phil. You need good compression, accurate timing and really well set up carbs to achieve it in my experience. Mine had just been completely refreshed inside, new rings but not a rebore, new bearings and a bank of carbs that were as clean as a whistle. Timing was set using a dwell meter and a good strobe. It was exceptionally quiet. Started it up once at Matlock Bath and I could hear people in the crowd around the bike asking if it was running and they were only 6-7 ft away.
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I’m just happy if it starts and gets me out and back without too much fuss!😂 I must say I’ve never heard these old bikes idling at 500 but it sounds impressive to get them tweaked to perform to that level.
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I like an idle speed of around 1100 when warm on an old Honda.
At under 700 rpm they never sound happy imho.
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At under 700 rpm they never sound happy imho.
An pro Honda mec told me: they're not all alike, for some reason that we don't know, some will never idle happily @ < 1000 rpm.
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Although I can get it to idle at 500, it's set at 1000
Sent from my moto g(50) using Tapatalk
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As Bryan says, put the original jets/needles etc back in, aftermarket jets are quite frankly awful, poorly made, lack of precision etc. Especially the float seat parts, they leak for fun as a rule.
I wonder from where the guy at classic octane sources his ‘kits’. He never seems to have any issues…..or does he🤔
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In my experience, the Japanese Keyster kits have worked for me when I have not been able to use original brassware - which I prefer to use. Had to use Keyster float valves on a few rebuilds and they have been fine. It's the cheap Chinese kits that are rubbish
Sent from my moto g(50) using Tapatalk
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There are more like Classic Octane. I can't take them serious.
It's the usual American bragging:
"But before I demonstrate how to set the ignition on a CB500 or 550, I wanna show you guys my new blasting cabinet that arrived from Amazon today and-it-is-aw-some."
And then later he ofcourse forgets to even mention the checking cq adjustment of the breakerpoints gaps and goes to twisting the plates rightaway.
In general Commonmotors has some good instructive videos, although I disagree on some details.
For carbs (either CB350F/400F or CB500/550) Motormac at Youtube is best. Language is German. Only he should not have fitted Keyster parts imo, be it that he's gründlich enough to show us the difference in dimensions between OEM and Keyster float valve sets.
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[...]This is the video I followed: https://www.youtube.com/watch?v=JFTOfYl5BSc&ab_channel=ClassicOctane.
The best on the subject is Motormac. On Youtube: Motormac Honda CB500 four Vergaser. You don't have to see all of them. Language is German. But he's the best.
[...] Would you suggest that I clean the bowls again?
Personally I'd refit the original parts. Mine ran 140.000 km and still don't wear.
I've not touched the thumb screw in any way since I've bought the bike. So I guess I'll try it tomorrow.
That should be the first step. Who kniws? Aim at an idle of 1150-1200 rpm.
Thanks for your valuable input!
Today I've managed to get the engine to idle at 1000 rpm by simply turning the thumb screw. I've made 3 videos that explain some concerns.
Video 1: https://youtube.com/shorts/sF54YTm3NVY?feature=share
After starting the engine with choke closed, the engine idles at 3000 rpm with choke open. When I close the choke again, the engine instantly stalls. Is this normal?
Video 2: https://youtube.com/shorts/Bz4SHuQANso?feature=share
I turned the thumb screw and managed to get the engine to idle at 1500 rpm. But when I use the throttle, the engine got stuck in a high idle at 3000 rpm.
Video 3: https://youtube.com/shorts/NGVH7g6JEZg?feature=share
By further turning of the thumb screw, the engine idles around 1100 rpm. However, there is a sound coming from the engine that doesn't sound that good. Also, after throttling the engine almost stalls.
How do I proceed from here?
Cheers!
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This is characteristic of impaired low speed/idle circuits, they should take responsibility for this very rpm range but when limited in their delivery the carburettor needs you to open the throttle more to get fuel from the main jets and needle delivery.
Classically, you'll ordinarily just go round and round again and again by adjusting the "thumb" screw to reposition the main slides, but never get anywhere conclusive.
The poor sound when running lower rpm is because all of tge cylinders are not firing (no fuel from idle on some) that just rattles the chains and components inside.
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Just use the fast idle screw, can do it with your gloves on. Never understood the 'race to the bottom' with idle speeds myself
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[...] Never understood the 'race to the bottom' with idle speeds myself
Neither do I.
Here's a fine CB550 from Honda's Collection Hall which seems to idle at 2000 rpm. I am used to raise the idle to 2000 rpm myself after a cold start to reduce it to say 1150 a km further on. I am with the legendary Carl Hertweck, who was in favor of fast idling.
Mine shifts just as easy @ 2000 as @ 1100.
https://www.youtube.com/watch?v=Z4GYMDP7Jtk&t=90s
Just don't rev to 8000 as in the vid.
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Siloxious, here's a simple check for the idle circuits.
Have the engine 'idle' at a rpm, where it's steady. Then turn with a screwdriver the airscrew of carb #1 all the way in (gently!) and wait 15 seconds and then to three turns out and wait again. There should be a change in rpm. This change can be a minor one, so listen carefully. Reset the airscrew to its former position.
Repeat this for carb #2, and then #3 and finally #4. The carb that does not give a change in rpm, has an issue in the idle circuit. Don't forget to wait some 15 seconds after each change.
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Or just ride it….
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If he’s so legendary why have we never heard of him. Seriously, one person says something and you latch onto it as gospel.
There is no race to the bottom Peter, it’s about setting the engine up to what the manufacturer recommended. Increasing the tickover to compensate for faults or problems in the engine is like sticking your fingers in your ears because you don’t like listening to something, ultimately it’s pointless. The problem here is that the idle screw isn’t the answer, fixing what’s causing the problem is the answer.
Those carbs have clearly been apart and whoever did them clearly didn’t know what they were doing.
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@ Siloxious Just to satisfy my curiosity, when you set the timing of the ignition, did you first check the breakerpoints gaps?
As far as the carbs.
1.Verify fuellines have the right dimensions
The CB500/550s are very sensitive for a proper fuelflow route, so let us first establish whether everything is standard or not.The correct dimensions for the fuellines are: for the CB500 and earlier CB550s: 18 and 30 cm length for the models with the bowltype petcock and 17 and 28 cm for models that have the newer style petcock. Do not be tempted to have them longer. For the tube that supplies carbs 3+4, use the soft metal clamp in the middle front side as shown in the pic (btw, horizontal is good enough) for proper routing. Ideal inside ⌀ of the fuel lines is 5,5 mm. Outside ⌀ will be around 10mm. Have this and the lines will not kink. Abstain from extra inline filters. Some have been lucky with them, but my experience is they can't be trusted. Often it isn't that filter itself, but the rerouting of the fuel line that - sometimes intermittent - impedes a proper delivery of the gas.
2. To be sure, all four carbs receive the same amount of fuel, read this: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647 When you do this test, realise it takes quite some time before the bowl is filled completely.
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If he’s so legendary why have we never heard of him.
Oh Sir, there's a whole continent east of you.;D
Seriously, one person says something and you latch onto it as gospel.
Why such an accusation, Oddjob? Should we latch onto what you say instead as a gospel? Hertweck has lead Das Motorrad for years. You may not know this, but it is the biggest and best motorcyle magazine in Europe and maybe even the world. In the 70s it was spelled by Honda. Many grew up with Hertweck's publications. He is not the only one who prefers a somewhat raised idle...
You seem to forget that I had mine idle nicely at a true 800 rpm, but was advised to increase it to 1000 or 1100 by someone who knew much more than me. I've learned a lot from him. Why would I deviate from what he and Honda says and possibly end up with fouled plugs? I'd rather stay on the safe side. I'm not in the category of those who prefer sitting in a deckchair next to their bike listening to an idling engine over riding it. Youtube has lots of vids where bikes idle for too long. It's generally considered good advice (and certainly no gospel) to idle as short as possible and start riding. That's what the bike is for.
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I didn't say follow my advise, I said HONDA said it, as they made the bike I think they know more about it than anyone else.
Never heard of Das Motorrad and TBH I don't take advise from magazines as they have an agenda, they need to sell advertising space so they say whoever is paying them to say generally.
How can I forget it idled at 800, you've never mentioned to my knowledge, plus I didn't say at anytime to idle the engine at that speed, just that if the engine can idle at that speed it's a good indication of the state of the engine, mine would but mine idled at 1000 normally. 1000-1100 is close enough to what Honda specified, anymore is not necessary IMO.
The rest of your reply is just off topic so I won't bother answered that.
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@ Siloxious Just to satisfy my curiosity, when you set the timing of the ignition, did you first check the breakerpoints gaps?
As far as the carbs.
1.Verify fuellines have the right dimensions
The CB500/550s are very sensitive for a proper fuelflow route, so let us first establish whether everything is standard or not.The correct dimensions for the fuellines are: for the CB500 and earlier CB550s: 18 and 30 cm length for the models with the bowltype petcock and 17 and 28 cm for models that have the newer style petcock. Do not be tempted to have them longer. For the tube that supplies carbs 3+4, use the soft metal clamp in the middle front side as shown in the pic (btw, horizontal is good enough) for proper routing. Ideal inside ⌀ of the fuel lines is 5,5 mm. Outside ⌀ will be around 10mm. Have this and the lines will not kink. Abstain from extra inline filters. Some have been lucky with them, but my experience is they can't be trusted. Often it isn't that filter itself, but the rerouting of the fuel line that - sometimes intermittent - impedes a proper delivery of the gas.
2. To be sure, all four carbs receive the same amount of fuel, read this: http://forums.sohc4.net/index.php/topic,185754.msg2151647.html#msg2151647 When you do this test, realise it takes quite some time before the bowl is filled completely.
I’ve just checked the ignition timing statically and the bike idles good at 1100 rpm. As I have not a lot of time today, I’ll check the carbs tomorrow. Thanks for your advice!
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I have heard of Das Motorrad from when I worked in Germany many decades ago.
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I have heard of Das Motorrad from when I worked in Germany many decades ago.
Das Motorrad is big in Germany and German speaking countries like Austria and Switzerland. I don't know about now, but it used to be in Dutch kiosks as well. They carry out tests of products with typical German Gründlichkeit and - being so big - they can pay for laboratories when needed.