Emisions

[markmark2]

Hi all, car passed MOT today with no issues. Got the emissions checked although its not a requirement on a 74. I know its running a bit lean. Could somebody interpret these figure please and is it worth adjusting the mixture?

CO 1.76
COcor 1.99
CO2 11.5
Lambda 1.129
HC 175
O2 3.73

Cheers Mark

[Tim Ward]

Mine the other day for example was CO 5. HC 450. Apparently you are allowed HC up to 1200. The MOT tester said that the old cars do smell as if they are running a bit rich, as they have no catalytic converters. Tim

[markmark2]

Mine the other day for example was CO 5. HC 450. Apparently you are allowed HC up to 1200. The MOT tester said that the old cars do smell as if they are running a bit rich, as they have no catalytic converters. Tim

Hi tim, I'll assume that low is good then?

[Tim Ward]

My thoughts are your CO is too low. I think the book figures when new was around 2.5 to 3. that was before wear in the jets had taken place. I am sure somebody else will have some thoughts on it as well.

[markmark2]

[QUOTE=Tim Ward;380155]My thoughts are your CO is too low. I think the book figures when new was around 2.5 to 3. that was before wear in the jets had taken place. I am sure somebody else will have some thoughts on it as well.

Do you know what that means?

[markmark2]

My thoughts are your CO is too low. I think the book figures when new was around 2.5 to 3. that was before wear in the jets had taken place. I am sure somebody else will have some thoughts on it as well.

Dont really understand it. Would be great if somebody could explain what it all means and what needs to be done.

[Tim Ward]

you need to adjust the carbs with a tool to make the CO a bit higher. Might be worth taking it to a garage that specialises in classic cars

[KOY 23]

Have you the original carbs?

[markmark2]

Have you the original carbs?

They are strombergs, I doubt they are the original to the car tho. Are these figures suggesting that it is just running a bit weak? Thanks Mark

[Stagdad]

1.129 lambda is about 16.5:1 AFR , idle is usually set a tad rich something like 13.5:1 to 14:1 , so yours looks to be quite lean if that figure is correct.

[markmark2]

1.129 lambda is about 16.5:1 AFR , idle is usually set a tad rich something like 13.5:1 to 14:1 , so yours looks to be quite lean if that figure is correct.

Thank you stagdad, thats what I needed to know. Would you say a 1/4 turn richer on each carb would suffice or 1/2 turn? Thanks again Mark

[flying farmer]

Do you know what your current fuel consumption is?

It is definitely too lean, so give them quarter of a turn each. Fuel consumption should not suffer until you get too rich, and you might notice better throttle response.

If you don't know what your current fuel consumption is, then you are really shooting in the dark.

Don't assume that just because it is correct at idle, that it is correct anywhere else due to carburettor wear. There have been a few posting on here that they have to wind the mixture weak for the MOT then put it back to improve driveability, though it can work the other way as well.

If quarter of a turn improves things you could then try a bit more and again keep an eye on the fuel consumption.

Neil

[markmark2]

Do you know what your current fuel consumption is?

It is definitely too lean, so give them quarter of a turn each. Fuel consumption should not suffer until you get too rich, and you might notice better throttle response.

If you don't know what your current fuel consumption is, then you are really shooting in the dark.

Don't assume that just because it is correct at idle, that it is correct anywhere else due to carburettor wear. There have been a few posting on here that they have to wind the mixture weak for the MOT then put it back to improve driveability, though it can work the other way as well.

If quarter of a turn improves things you could then try a bit more and again keep an eye on the fuel consumption.

Neil

Hi Neil, thanks for the reply. To be honest, Ive never been one for checking fuel consumption. I just put fuel in when its required. I will give it a 1/4 turn and then keep an eye on the colour of the plugs. Thanks again. Mark

[wilf]

You won't be able to tell much from the colour of the plugs as unleaded does not give anywhere near the same plug colours as old leaded. Just a rough guide these days.

[Guest]

The Stag engine is perfectly capable of running nice and lean, thanks to the wedge head design.
Just because a car doesn't have a catalytic convertor doesn't mean it's creating loads of pollution.

An HC figure of only 175 is really exemplary for a 30 yr old car.
If the car shows no signs of missing cylinders and gives good torque, leave well alone.