Sooty plugs.

[Johnny4428]

Now I am sort of giving myself a kick up the arse here. I had a nice run out yesterday on the k3 but quickly realised only 3 cylinders were firing. This is the second time this has happened to me this year on this bike. I got back home and checked cyl 2 and the plug was just sooted up then checked the rest and they were all sooty. Then the penny dropped that I had replaced the pilots with 45’s instead of 42’s but had made no compensating adjustment to mixer screws. As most of my running around here is in the lower to mid range rpm it stands to reason that it is getting slightly too much fuel! The reason I changed the pilots was to improve cold starting which it did do. So today I will make an adjustment to the carbs and take for another run, since it is a nice day.

[deltarider]

What bike?

[Johnny4428]

550k3

[Johnny4428]

Just a follow up, had a run out this afternoon probably about 40 miles or so having reset screw to one turn out. Bike was running great. After returning to base I checked the plugs again. There was a bit of improvement, no4 was a nice colour while 1 2 and 3 was a bit black still. Now reduced these screws by a further 1/4 turn. Will see how the next run goes.

[Sesman]

Hi, Johnny.

Out of interest which carbs are you using and what size main jets are installed? I presume you are running with the standard airbox, using a standard exhaust?

[K2-K6]

At least you're getting a response Johnny, an indication that those circuits are operational.

I'm presuming PD carbs, with screw adjust on engine side of throttle slide ?

Honda manuals for slightly later carbs (I've not seen K3 manual) give very specific routine and details for setting these adjustment.

Furthermore, they indicate that factory settings are individual down to each carburettor, then if the carbs are stripped and reassembled, there's need to pass through that routine as factory, subsequently record the final setting position by nothing in the service notes as baseline from there onwards.

They are not "set all adjustment the same" carburettor, that's not accurate enough.

This is where the fine adjustment of idle "synchronization occurs and not the syncing that everyone focuses on. The workshop synchronization just sets the slide air parity, being too course an adjustment to fine tune idle fuelling.  Its a part of the process, but not the whole process. Fine combustion parity comes from then making adjustment to these idle circuit flow when everything is set correctly. 

Even fuel injection system mirror this aspect on more sophisticated installations.

[Johnny4428]

Hi, Johnny.

Out of interest which carbs are you using and what size main jets are installed? I presume you are running with the standard airbox, using a standard exhaust?

It’s a standard set up with 4 into 4 pipes and factory air box set up with oil breather recovery thingy.
The carbs are PD46A with standard mains.

[Johnny4428]

At least you're getting a response Johnny, an indication that those circuits are operational.

I'm presuming PD carbs, with screw adjust on engine side of throttle slide ?

Honda manuals for slightly later carbs (I've not seen K3 manual) give very specific routine and details for setting these adjustment.

Furthermore, they indicate that factory settings are individual down to each carburettor, then if the carbs are stripped and reassembled, there's need to pass through that routine as factory, subsequently record the final setting position by nothing in the service notes as baseline from there onwards.

They are not "set all adjustment the same" carburettor, that's not accurate enough.

This is where the fine adjustment of idle "synchronization occurs and not the syncing that everyone focuses on. The workshop synchronization just sets the slide air parity, being too course an adjustment to fine tune idle fuelling.  Its a part of the process, but not the whole process. Fine combustion parity comes from then making adjustment to these idle circuit flow when everything is set correctly. 

Even fuel injection system mirror this aspect on more sophisticated installations.

Yes Nigel the screw on the engine side. What you have written above makes complete sense and I have to walk away from trying to get these multi carb set ups all set the same. I’m quite happy to have one screw at 3/4 and the other three 1/2 turn out if that’s what it takes! 😜

[K2-K6]

Thought I'd copy this text to thread that I've included in another

 "While I can see the reasoning, I think this deserves expansion to understand.

The amount of fuel added to the air going under the slide at idle us adjusted by the routine that Honda gives for setting airscrew idle mixture.  In other words it can't be wrong if its set correctly.

It can go wrong if set badly, or IF the idle circuit, both jet and screw controlled air passage, change after its been correctly set.

In effect, you can't get too much gap under the slide as it should always be proportionately accompanied by the correct amount of fuel. This is exactly what the idle circuit is for.

I intend discussing in carb thread, when I get to this bit

That Honda routine specifically targets fuel air ratio delivered by the idle circuit against the set position of the slide. If that setting then becomes inappropriate, the mixture, for that cylinder, moves out and away form how you've set it and usually lean with the fuel jet orifice being compromised. So you do get too much air, but not from overall position of slide, but failure of delivery fuel jet to maintain flow at defined rate.

To make clear , and I'll shout this bit    THERE'S NO REQUIREMENT TO SET THE AIRSCREW EQUALLY ..... THE HONDA METHOD VERY SPECIFICALLY TARGETS PARITY OF COMBUSTION AND ACCEPTS DIFFERENT SETTINGS FOM CARB  TO CARB ON THE SAME ENGINE.

If you carry out the setting routine to the manual description, it will "show" you if there's any impairment in that specific circuit by needing a setting that just doesn't fit the expected.
It does this by you making observations of the fuel air ratio as you turn the screw and listen to the combustion.

That must be one of the most under used parts of their manuals .... but so important in setup.

Everyone goes straight to carb synchronization, missing the substance and reasoning contained within this little routine that they give."

To emphasise, it's a very innocuous instruction written into manuals by Honda, but absolutely fundamental in their setting i believe.

It brings the combustion process to breakdown from being too lean, then instructs to move it back from that point toward richer in creating a competent base point .

It may look like a single until four cylinder engine, but really its a "platoon" of near 125cc singles on a common crankshaft, thats from a carburettor point of view.

Their routine effectively contains a "calibration" of each carburettor idle system, taking into account any production tolerance that may be included in manufacture of the parts.

Its very highly likely they'll be different from one to another when settings are finely resolved.

[deltarider]

Thought I'd copy this text to thread that I've included in another

 "While I can see the reasoning, I think this deserves expansion to understand.

The amount of fuel added to the air going under the slide at idle us adjusted by the routine that Honda gives for setting airscrew idle mixture.  In other words it can't be wrong if its set correctly.

It can go wrong if set badly, or IF the idle circuit, both jet and screw controlled air passage, change after its been correctly set.

In effect, you can't get too much gap under the slide as it should always be proportionately accompanied by the correct amount of fuel. This is exactly what the idle circuit is for.

I intend discussing in carb thread, when I get to this bit

That Honda routine specifically targets fuel air ratio delivered by the idle circuit against the set position of the slide. If that setting then becomes inappropriate, the mixture, for that cylinder, moves out and away form how you've set it and usually lean with the fuel jet orifice being compromised. So you do get too much air, but not from overall position of slide, but failure of delivery fuel jet to maintain flow at defined rate.

To make clear , and I'll shout this bit    THERE'S NO REQUIREMENT TO SET THE AIRSCREW EQUALLY ..... THE HONDA METHOD VERY SPECIFICALLY TARGETS PARITY OF COMBUSTION AND ACCEPTS DIFFERENT SETTINGS FOM CARB  TO CARB ON THE SAME ENGINE.

If you carry out the setting routine to the manual description, it will "show" you if there's any impairment in that specific circuit by needing a setting that just doesn't fit the expected.
It does this by you making observations of the fuel air ratio as you turn the screw and listen to the combustion.

That must be one of the most under used parts of their manuals .... but so important in setup.

Everyone goes straight to carb synchronization, missing the substance and reasoning contained within this little routine that they give."

To emphasise, it's a very innocuous instruction written into manuals by Honda, but absolutely fundamental in their setting i believe.

It brings the combustion process to breakdown from being too lean, then instructs to move it back from that point toward richer in creating a competent base point .

It may look like a single until four cylinder engine, but really its a "platoon" of near 125cc singles on a common crankshaft, thats from a carburettor point of view.

Their routine effectively contains a "calibration" of each carburettor idle system, taking into account any production tolerance that may be included in manufacture of the parts.

Its very highly likely they'll be different from one to another when settings are finely resolved.

As usual I have read your post with much interest. A few remarks if you will allow me. I don't know what Honda manual you refer to, but the 'Honda method' is definitely not in the CB500/550 Shop Manual. In that manual the airscrew setting data is not even consistent. On one page it is 1 turn +/- 1/8, on another 1 +/- 3/8. The content of your post is in theory correct ofcourse, but in practice it's almost impossible to perform the method with good results and so far I have I not seen a video on Youtube or whatever channel that demonstrates the method succesfully. I find that telling and I invite anyone to make one. Over the years I've 'played' with my airscrew openings quite a bit and let me confess that I find it extremely difficult to arrive at an optimum. I should never have touched them on that campground in Greece in 1980. Have a look at the pic below. It shows the scale of an exhaust gas analyzer, typical for that era. As you can see, the yellow field is quite extended and I doubt such a meter can be of much help. To my knowledge Honda did not specify what % CO to aim for (idle) for our models. Monitoring manometers whilst synchronizing, won't help you either. Increments of even half a turn will not result in a changed underpressure of that cylinder. The only thing I can think of, is to put, after syncing your carbs, a rubber hose in the exhausts and listen carefuly and see if you, by comparing and turning the airscrews, can arrive at identical sounds of all four. A leaner carb will produce a lighter sound than a richer which has a much fatter 'thump' sound. If someone has managed a perfectly mixture at idle CB500 4-4 and - more  important - a linear acceleration*, I welcome a video with a good recording of the sound that can serve us all as a benchmark. 
* As far as the CB500 model for the European continent, I read the slow jets as auxiliary jets that happen to double as idle jets

[K2-K6]

Agree about the meter, looks to be a "prediction" or air fuel ratio based on measurement of CO.

Ordinarily they were calibrated in clear air to give zero reference point for CO , then would read total amount available (by comparison to that ref) of content in exhaust flow.

Could be used with interpretation for some adjustments, but maybe not an absolute in analysis of what we'd need to know.

Another member on here with access to test station (annual MOT inspection) put a 500 on test for each pipe, then with a much more useful sweep of data available, we could see more of the status. I'll try tomfind posting.

There's good reason why most current vehicles use O2 sensors to monitor this aspect of combustion.

One of the test regime parameters in UK is HC, hydrocarbon level, which is very useful as it shows the unburnt content of fuel coming down the exhaust, allowing much more insight into just how much of the fuel ingested is being burnt or passed out of the chamber unused.

[deltarider]

[...]
Another member on here with access to test station (annual MOT inspection) put a 500 on test for each pipe, then with a much more useful sweep of data available, we could see more of the status. I'll try tomfind posting.[...]

Thanks. I am very, very interested in that member's findings. I found a similar CO exhaust gas analyzer that I have repaired. It's far from a professional tool, but it was used in that era by amateurs in the US and possibly UK. The working principle is: two thermal conductivity cells, one for measuring the resistance of the ambient air, the second for the resistance of the exhaust gas.The comparison is made by a Wheatstone bridge, so think milliamps that activitate the dial. It's far from easy in use. It takes some 15 min. to warm it and then you need to calibrate the instrument by setting the dial in the exact middle of the scale. That can easily take another 10 minutes.
All in all I found it very timeconsuming. After removing the pickup tube from one pipe, I had to calibrate the instrument again before bringing the tube in the second pipe. I want to give it a second try but then at 2500 rpm first. My first objective is to arrive at identical readings at the 4 pipes by finetuning the airscrews. Then at least I have a starting point for when I lower the rpm to say 1100.
My experience with similar 'solid state' instruments for the consumer market of that era is: they work OK, but they are far from rugged; cables, cell and the instrument itself are very flimsy. Mine is no exception and very easy to damage

Another thing although unrelated. In a experimentive mood I once connected 4 tubes from the 4 underpressure ports in the manifolds to eachother to see if it would make a difference in running. I found no difference. My question is: why not? BTW, Rob van Gulik has that same set up on his CB400F.

[K2-K6]

This took some finding as I could remember it but not topic link words 

https://www.sohc.co.uk/index.php/topic,18831.0.html#msg165543

Some interesting figures in there.

[deltarider]

Thank you for looking it up. Looking at the low CO, I can guarantee you that no standard CB500 will ever run well with those low figures. It will run no doubt, but driveability will be out of the window. Expect at least 4 - 5% CO, for any bike of that era, some even 6% to run well. I've discussed this many years ago with a specialist who runs a business (Dyno tests) and has succesfully cured many bikes like the CB550K3. I even judge the % CO set for that CB400F (2% @ idle and 3% @ 4000 rpm in this English article is not enough. A KTM mechanic I recently talked to, suggested even for the one cylinders he trades 4,5% for a good running engine.

[K2-K6]

Probably worthwhile posting the results in this thread

"Quote
Well, I popped into work today for something else and checked the bike while I was there. At idle, I got the following.

                      Cyl 1       Cyl2       Cyl3        Cyl4
CO                    2.0        1.8          2.0         3.3
CO2                  2.6         2.3         2.3         3.2
Lambda            2.7         3.3         3.0          2.1
HC                  840          293       600         335
O2                  15.2         15.5      15.5        13.1

At approx 4000 rpm

CO                    3             3            2.2           4
CO2                  2             2            2.2           3
Lambda           2.5           2.7         3              2
HC                  900          310        110        250
O2                  14             15.6       15          13

Going by the HC values, it is running rich, a lot, especially No 1. Will try float levels first and a general tune up, valve clearances (assume to be standard). Running dyna coils and dyna ignition and non ressistant caps and plugs. Perhaps a new set of resister plugs, but will do a search to see if these are required with this set up"


The low CO appears to be not from setting fuel input that low though.

It looks to be the result of not burning the fuel it's given in the first place, that's shown by the high HC (unburnt fuel content in exhaust) which could be influenced by that engine spec. A "wild" camshaft is not good at low rpm, also a reduction of practical/dynamic compression ratio that will affect how the combustion is completed.

This is a known limitation of increased inlet cam timing and overlap with exhaust to be ineffective at low rpm. The dynamics coming together with exhaust and intake inertia at high rpm is what they are aimed at.

Unfortunately we've got no further assessment to give more consideration in what's really happening in that instance.