Stag emmissions

[Stagmatt254]

Hi,

I have recently accuired an old mot type exhaust gas analyser (sun DGA 1800) with a view to tuning the stag. As far as I can tell the machine works okay and gives reasonable readings on my everyday car. However when on the stag I am getting CO of 0.8 and a HC of 2500ppm. I was expecting a CO of around 3-4%. Stag runs okay and if anything I suspect it is a little rich. Can anyone offer any logic to this low CO figure or does it simply mean my gas analyser is Knackered (which I don't think it is). Next question are there any sun DGA experts out there ?

Any advice please

[Stagdad]

http://www.perfectpower.com/index.php?option=com_content&view=article&id=14&Itemid=17

Looks like you are very lean at about 14:1 .If you use a bit of choke out when pulling away does it improve performance?

I would say mine is set up pretty good and I have an air fuel wide band sensor fitted, it idles between 12.5:1 and 13:1


Cheers Steve

[Stagmatt254]

Hi,

To be honest it gets away fine and runs okay which is why I am puzzled. If I pull the choke whilst on the analyser the CO rockets up as you would expect but it is clearly rich, hunting black smoke etc. Also the plugs seem about the right colour.

[72BLUE]

I took my Stag to my local garage after I bought it for a sneaky free Co check. It was only 11%

Still have not tuned it yet as on the way back home my wiring loom caught fire

Cheers, Keith.

[jleyton]

Talking about mixture etc, my car always (famous last words) starts instantly from cold, with the choke and then I can IMMEDIATELY push it back in. In fact it splutters from being too rich if I leave it out at all.

Well, that all pointed to it running too rich but the plugs are a perfect colour and my MOT centre checked CO2 at just under the limit (2 or is it 3% ?)

I'm perfectly happy with the situation but a bit mystified

Any thoughts guys ?

Cheers

Julian

[Stagdad]

Twice

[Stagdad]

I think it's 4 percent on the older stags until older than 75 then it's just smoke ttest cheers Steve

[jleyton]

Thanks Steve and a good point.

Do you, or other, experience the same as me ? Ie, no need for choke after starting ?

Cheers

Julian

[elvimto]

I do almost the same Julian and my car is inside a warm garage, since i do not have to meet emissions but would like to do my part to keep global warming at bay I have been tweaking the carbs to lean it out a bit seems to be running fine for now. I would try and get the machine checked for calibration if its out then its no good to you.

cheers stuart

[Stagdad]

No I need a small amount for a while Julian.

[jleyton]

Thanks Steve.

Stuart, it was the MOT station's tester but the thing I remain surprised about is that my plugs look a perfect colour - suggesting the correct mixture

Cheers

Julian

[wilf]

Plug colour will be more affected by part and full throttle running conditions, what you are looking at is tickover mixture, and a whole raft of issues can affect that, inluding worn jets/needles etc.

[flying farmer]

As Wilf says plug colour is more of a driving than idling issue. When I fitted the carbs that came with my Stag to the Stag engined Estate, the mixture was ok at idle according to the gas analyser, but cold running and starting problems led me to discover one carb was too rich and the other too lean.
Having sorted that I found the mixture was all over the place up and down the rev range and at different constant speeds.
(I have a lambda sensor fitted in the exhaust and a plug in gas analyser which helps here)
New needles , jets and float chamber valves were fitted and mixture is now consistant through the rev range, but it does take a couple of miles before I can push the choke fully in.
The reason your analyser is showing relatively high hydrocarbons and low CO is that the mixture is so weak some of the fuel is going down the exhaust unburned. A missfire at idle will have the same effect.
Assuming you do not have a missfire, then I would leave well alone as the mixture could well be ok in the actual driving range
Neil

[DJT]

Thanks Steve and a good point.

Do you, or other, experience the same as me ? Ie, no need for choke after starting ?

Cheers

Julian

Fully out, no throttle - starts first time. Almost immediately push choke in to about 1/4". Keep it there for the first 1/2 mile if in stop-start traffic (1 mile if really cold), otherwise right in as soon as I have turned the corner at the end of the road (250 yards).

[Guest]

Ditto DJT's starting experience, except that it takes a bit longer (about 2 km) before I can push it fully home, otherwise it will stall if I stop.