Using Gunson Gastester on 74 2500M
Discussion
Guys, do any of you have any experience using one of these? I bought one long ago and thought I'd try it as part of my efforts to tune my 2500M.
I guess I'm a little dense, because after reading the instructions a few times, I'm still unsure what reading I should be tuning to.
I understand the Gunson reads CO level, but I don't know what level I should be aiming for. Anyone know?
Ron
I guess I'm a little dense, because after reading the instructions a few times, I'm still unsure what reading I should be tuning to.
I understand the Gunson reads CO level, but I don't know what level I should be aiming for. Anyone know?
Ron
Off the top of my head ... this could be wrong....
at normal idle speed.
modern EFi systems 0.5 - 1% CO
Older EFi systems 1 - 1.5% CO
K series (280i) < 2% CO
carbs < 4% CO
Try and get it as low as possible with engine still running sweetly - carbs won't get as low as EFi systems, I think you should be able to get to 2.5% ish for carbs ??
It's a long time since I fiddled with carbies !
at normal idle speed.
modern EFi systems 0.5 - 1% CO
Older EFi systems 1 - 1.5% CO
K series (280i) < 2% CO
carbs < 4% CO
Try and get it as low as possible with engine still running sweetly - carbs won't get as low as EFi systems, I think you should be able to get to 2.5% ish for carbs ??
It's a long time since I fiddled with carbies !
Edited by RCK974X on Thursday 22 December 04:26
Andy, thanks. Terrific information and very helpful as usual!
By the way, I found a website (for another exhaust gas analyzer) that made a comment to this effect;
A maximum CO content of about 2% corresponds closely to the ideal air/fuel ratio of 14.7. More, generally indicates too rich a mixture.
By the way, I found a website (for another exhaust gas analyzer) that made a comment to this effect;
A maximum CO content of about 2% corresponds closely to the ideal air/fuel ratio of 14.7. More, generally indicates too rich a mixture.
Glad it helped.
The official EFI numbers are always very low CO, as they do it for emmissions testing, and (typically) do run just slightly weaker than ideal.
Some EFi systems have a 'lean cruise' mode too, which pushes economy up quite a lot.
I couldn't easily remember the carbs number, but glad to see I was about right !!
The official EFI numbers are always very low CO, as they do it for emmissions testing, and (typically) do run just slightly weaker than ideal.
Some EFi systems have a 'lean cruise' mode too, which pushes economy up quite a lot.
I couldn't easily remember the carbs number, but glad to see I was about right !!
I remember reading somewhere on the internet about the setup when I was looking into it for ours.
I found someone who was testing it against an MOT gas tester, and he found that when the gunson was setup as per the instructions, to 2% in air, it read 2% higher than the MOT machine.
I've never really found out on ours, as we've not got an MOT machine. But, we did set my car up using it, and it was fine on its MOT emissions test later on in the year, so it can't have been far off.
I'll have to remember to check it next time just after the MOT.
It gives you a good starting point atleast, especially on carb'd cars where you've got a higher value to play with rather than some number lower than 1%. IIRC the limit for carb engines on the MOT is 3.5% CO (or it might be 4%, can't remember which one,
).
I found someone who was testing it against an MOT gas tester, and he found that when the gunson was setup as per the instructions, to 2% in air, it read 2% higher than the MOT machine.
I've never really found out on ours, as we've not got an MOT machine. But, we did set my car up using it, and it was fine on its MOT emissions test later on in the year, so it can't have been far off.
I'll have to remember to check it next time just after the MOT.
It gives you a good starting point atleast, especially on carb'd cars where you've got a higher value to play with rather than some number lower than 1%. IIRC the limit for carb engines on the MOT is 3.5% CO (or it might be 4%, can't remember which one,
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