CB500 Four - engine cuts off in idle

[deltarider]

[...]
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.

[philward]

Although I can get it to idle at 500, it's set at 1000

Sent from my moto g(50) using Tapatalk

[Sesman]

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🤔

[philward]

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

[deltarider]

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. 

[Siloxious]

[...]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!

[K2-K6]

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.

[peterengland]

Just use the fast idle screw, can do it with your gloves on. Never understood the 'race to the bottom' with idle speeds myself

[deltarider]

[...] 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.

[deltarider]

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.

[Sesman]

Or just ride it….

[Oddjob]

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.

[deltarider]

@ 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.

[deltarider]

If he’s so legendary why have we never heard of him.

   Oh Sir, there's a whole continent east of you.

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.

[Oddjob]

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.