SOHC.co.uk Forums > CB500/550
Sooty plugs.
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:
--- Quote from: K2-K6 on October 09, 2024, 09:55:59 AM ---[...]
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.[...]
--- End quote ---
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 ;D
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.
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