Discussion
Nice it passed with flying colours through its MOT. That the CO can be that low is an indication that the whole engine and system to run it is healthy! (or you have an inlet air leak 
)
CO depends.... around 4 vol% for power (some even go to 5%), 3 vol% for a compromise and sufficient to pass MOT (think it should be less than 3.5%). All of this on a standard 3.5 with flapper.
Adjust clockwise at the AFM to increase CO as it makes the air bypass in the AFM smaller and less 'non metered' air make more CO.
Once had to unscrew the adjuster to its maximum to pass the MOT just. Later top tip on pistonheads to undo it completely and clean it. After that I could set idle rpm as I wanted and CO as well. Never tried CO below 3% on my wedge as too lean kills engines.....
Rob
)CO depends.... around 4 vol% for power (some even go to 5%), 3 vol% for a compromise and sufficient to pass MOT (think it should be less than 3.5%). All of this on a standard 3.5 with flapper.
Adjust clockwise at the AFM to increase CO as it makes the air bypass in the AFM smaller and less 'non metered' air make more CO.
Once had to unscrew the adjuster to its maximum to pass the MOT just. Later top tip on pistonheads to undo it completely and clean it. After that I could set idle rpm as I wanted and CO as well. Never tried CO below 3% on my wedge as too lean kills engines.....
Rob
Hi and thanks for the replies
The tester said I could take it back when he was less busy and use the co machine, so that's what I will do. I realise that it can't be set accurately without the correct gear but does anyone know roughly what effect say 1/4 or 1/2 a turn clockwise would have on the mixture as I would like to richen it up before I drive it any distance?
Also what should the warm tickover be?
Thanks again
The tester said I could take it back when he was less busy and use the co machine, so that's what I will do. I realise that it can't be set accurately without the correct gear but does anyone know roughly what effect say 1/4 or 1/2 a turn clockwise would have on the mixture as I would like to richen it up before I drive it any distance?
Also what should the warm tickover be?
Thanks again
which can be equally bad.350zWelgje said:
Never tried CO below 3% on my wedge as too lean kills engines.....
Really? Should i be worried with a tickover CO2 reading of 0.94 then? I have noticed the car is not as free to rev at the top end as it was before my engine tune. It really is quite different.
Could someone talk me through how i adjust the co2 on a 450 flapper just in case? Cheers
Jimbo
Never tried CO below 3% on my wedge as too lean kills engines.....
Really? Should i be worried with a tickover CO2 reading of 0.94 then? I have noticed the car is not as free to rev at the top end as it was before my engine tune. It really is quite different.
Could someone talk me through how i adjust the co2 on a 450 flapper just in case? Cheers
Jimbo
Correct that CO at idle doesn't say a lot...., to start even more confusion!
On flappers it is not only setting CO for idle, it does it throughout the full rev range based on it. So lean at idle means probably (but have no proof) lean at all times...
Best is a rolling road, but not having that or want to spend the money (on my standard engine) I just use the 3% as a reference just for myself (personal 80/20 rule logic). It is information and with 'wilder' and non-standard engines in TVRs I would not go about it that way and would have it setup properly.
Have a Gunson CO-tester to be sure my engine is tuned ok: I think it is worth the money, like to tune
my own engines, it saves me potential MOT agrivation and the cost for it to be setup at a garage. This tester doesn't cost a bomb, but it is only for CO and not full blown 4-gas etc., but on older engines it is all you need for exhaust gas tuning.
So perhaps an investment in a gunson CO-tester is the way forward.
Rob
On flappers it is not only setting CO for idle, it does it throughout the full rev range based on it. So lean at idle means probably (but have no proof) lean at all times...
Best is a rolling road, but not having that or want to spend the money (on my standard engine) I just use the 3% as a reference just for myself (personal 80/20 rule logic). It is information and with 'wilder' and non-standard engines in TVRs I would not go about it that way and would have it setup properly.
Have a Gunson CO-tester to be sure my engine is tuned ok: I think it is worth the money, like to tune
my own engines, it saves me potential MOT agrivation and the cost for it to be setup at a garage. This tester doesn't cost a bomb, but it is only for CO and not full blown 4-gas etc., but on older engines it is all you need for exhaust gas tuning.So perhaps an investment in a gunson CO-tester is the way forward.
Rob
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