I am trying to understand how CO2 reading influences the mixture. If I have CO2 set at for example 2% and I raise it to 5% will the fuel/air mixture go rich or lean? Asking as trying to adjust my 695 to best combo I can. Today when I connected it up it was at 7.5% (as it turns out flashing new DP map does not erase trim setting ). I have brought it down to 6% (give or take 0.1%) and not saying it is the best one but I do not want to get bike running lean as well. From manual service book reading is 1.5% to 3.5% while "Race reading" is 3.5% - 6%. Can someone explain? I have found idle adjustment screw and with 7.5% got it to idle at 850-900 RPM. It was hunting a lot but idling at cold even. When I dropped reading to 6% idle RPM went to 990-1040 with not as much hunting, it sounds even now. However when engine is cold the 850-900 is still my RPM and bike will now not idle at that so I have to use fast idle lever for a minute or so.
Here's a handy chart showing co to AFR CO% to Air Fuel Ratio (AFR) Table : How-To Library : The MG Experience The higher the AFR the leaner the mixture 14.7:1 is the stoichiometric (sort of ideal for best combustion) but in the real world 12:1 or 12.5:1 are the sort of figures quoted for max power. On my own bikes I have a co reading of 4.5 at the exhaust (12.83:1). So richer than stoichiometric.
That is a cool chart. Thx. BTW the other map also made it idle at 1500 hence me hitting the screw line. Quick one about gunson. It says to let it settle at 2.0% but my one is odd. I can go - 6% or + 1%. I think it is broken or something. I also read that when looking at its reading it is the reading - 2% base. Few guys on mini forum made a test and 2.5% on gunson was 0.5% at mot.
Luca I think it's CO not CO2. Stoichiometric in theory is when every last molecule of O2 mixes and burns the fuel. So not a molecule of fuel or air is left after combustion, only waste products. In the real world that can't really happen because you never get uniform mixing so some places in the chamber get too much O2 others not enough. As indicated in that table the lower the CO the higher A/F ratio. CO forms when there is insufficient Oxygen so the fuel constituents bond to one Oxygen atom rather than the stable pair. As soon as there is enough Oxygen around the CO degrades to the more stable CO2 usually shortly after it leaves the exhaust and enters the atmosphere. Normally there is excess fuel therefore you'll get CO as there is not enough Oxygen to go around. If you run excess air then combustion will become hotter as you will get full burning of the mixture. Its efficient but it can burn out engines. Funnily enough when working with gas turbines it appeared to be the opposite. They ran massive excess air around 13-15%, if the CO started to rise it was an indicator of either bad combustion or too much fuel. Its really the same thing the richer the mixture the more CO you will generate, with GTs you're just approaching it from the opposite direction. As far as gas analyzers go I used to work with power station gas analyzers quite frequently, both permanent and portable. These things were pretty fragile and recalibrated themselves usually every 6 hours using known concentrations from calibration gases. If running demonstration tests or conducting tuning, the analyzers were calibrated before and after each test, roughly every 2-4 hours. My point is even then you were looking at 2% accuracy typical and 0.5% best case, so gas analyzers are not the most accurate pieces of kit. Well that's my understanding of it, maybe somebody who knows more can chip in. John
Combustion is a compromise, ideally you want to be in the area of the Highest (put lowest by mistake) CO% and lowest HC (Hydrocarbons, this is unburnt fuel) what you are setting tho' is just the idle settings as I understand it? so not that critical, 3 - 5 % CO, or where ever it idles best.
Gunson say to set it to read 2% in air before going near the bike with it - leave it a while to settle to make sure it is steady. Done this way, my 916 runs well at around 5%, if I try 1 or 2% it spits (flames) back through the intakes.
I don't know the Gunson so I'm probably not qualified to really make any comment on it. However that seems a very strange statement. If you were in a 2% CO atmosphere I think you'd be in deep trouble, I think the normal concentration is around 0.2ppm Just me bumping my gums
I don't know why? but that's what they say. From the manual; "Allow a minimum period of eight minutes with the instrument probe in fresh air. Set the calibration control to achieve 2.0% on the CO range and observe the display for a further two minutes minimum to ensure that the reading has stabilized." http://gunson.co.uk/items/pdf/Products/G4125_booklet.pdf
I know I noticed that. Regarding Gunson. The 2% is a debate I found on the internet. No one understands why they say to set it at 2%. Then there are arguments that what you are reading in pipe should be X-2% then some say it should not. Some people even called manufacturer to confirm if manula is correct and valid which they said they did. On mini couper forum (seems the most informative info I found to date) a guy in US did his setup with Gunsun and at 2% air he set it run at 4.5%. Engien was hunting and failed its MOT as was spitting over 3%. He then set it again assuming 2% is 0 so set to 2.5% and got at MOT 0.5% and engien was runnign smooth. Then few other people did same and got same result. Only wway to fund out is for me to go to somewhere with professional CO tester and see what the bike is at. I set it to 6% me thinks. Also my Gunsun never reaches 2% in free air now and I do not know why. Best I get is 1.8% am I living in very clean part of Wembely? It did reach well over 2% before in free air.
Luca if you were breathing 2% CO you would either be sick or dead When I used to calibrate analyzers we would sometimes use atmospheric air as a test gas, not the best but sometimes you had to as it was all you had. If I was calibrating for CO I would zero the analyzer using atmospheric air. When actually doing hand over tests usually to EPA methods you would not only calibrate gain and offset you would run at least 2 midspan gases to prove the span was linear, that's how much the professionals trust them. These instruments were incredibly fragile and God help you if any moisture got into them from the sample. From that I think the guy on the Cooper forum is correct. However if you want to calibrate any instrument you need to determine both zero and Upper range in order that you calibrate both the gain and offset. Using one reading you just cannot do that. Cutting to the chase I put them in the same category as sound meters, not to be trusted!! John
How did this work out? I have just got a used Gunson gastester to address my farting air box issues. Do I use 2% as zero and set the mix to 6% to achieve the desired 4% What did other 1098 owners/users do diddly do?
You know what I never went to test it with professional as bike is not surging, idling nicely and not spitting out flame/bang noises. I made the setup basing air at 0% and then set it up at 4.5%. Not helpful I know but on one of those days I will go and do back to back reading with gansun and professional one to have a reference.
