Author Topic: CO% at idle on 350SE (M116.985) with K-jetronic  (Read 283 times)

Berggreen

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CO% at idle on 350SE (M116.985) with K-jetronic
« on: 11 April 2021, 04:03 AM »
Hello everyone

I am doing some fine tuning of the fuel mixture on my European model 350SE from 12/1977 with a M116.985 engine with K-jetronic.

I can see in the service manual that the standard fuel/air mixture setting in idle while measuring the exhaust CO% is 0.5-1.5.

But with that said, and as these exhaust limits were probably also stated in order to comply with various exhaust emission regulations in Europe, what do you recommend I tune the car to, in order to obtain the best compromise between performance and fuel consumption?

Hope you can help. :)

Cheers,

Christian
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

ptashek

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #1 on: 11 April 2021, 04:18 AM »
Different engine, but a data point nevertheless ;)
My euro M117.986 is tuned to ~1.4% CO.

Pulls like a bear, and fuel consumption wise is within factory spec. Doesn't run hot, and spark plugs are nice and clean.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE (history, resto)

Type17

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #2 on: 11 April 2021, 11:07 AM »
My '76 350SE (M116.985) runs best around 1% CO.


It was running a bit rich when I first got it (about 3% if I remember), and was actually more sluggish and idled less smoothly until I corrected it.


On a previous car with K-Jet (VW Golf 1 GTI), the same was true. Being young, I tried different CO levels to see what was quickest (Emissions tests for the car at that time allowed up to 4.5%), but found that 1 - 1.5% was the best for torque.

Berggreen

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #3 on: 11 April 2021, 12:03 PM »
My '76 350SE (M116.985) runs best around 1% CO.


It was running a bit rich when I first got it (about 3% if I remember), and was actually more sluggish and idled less smoothly until I corrected it.


On a previous car with K-Jet (VW Golf 1 GTI), the same was true. Being young, I tried different CO levels to see what was quickest (Emissions tests for the car at that time allowed up to 4.5%), but found that 1 - 1.5% was the best for torque.

Thanks a lot! Great advice! :)

Currently, I have mine at 2.5%CO and it is a bit unstable at idle.

What rpms do you have in idle in P?

Do you se a shift in rpms between P and D?

Cheers,

Christian :)
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

Berggreen

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #4 on: 11 April 2021, 12:05 PM »
Different engine, but a data point nevertheless ;)
My euro M117.986 is tuned to ~1.4% CO.

Pulls like a bear, and fuel consumption wise is within factory spec. Doesn't run hot, and spark plugs are nice and clean.

Great, thanks! I can hear that I need to lean it a bit. :)

Cheers,

Christian
02/1971 MB 280SL (aut.) - olive green 291H
11/1970 MB 280SL (man.) - silver 180G
12/1977 MB 350SE (aut.) - deep green 825H
03/1969 Volvo 1800S (man.) - dark green 94

Type17

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #5 on: 11 April 2021, 12:11 PM »

What rpms do you have in idle in P?

Do you see a shift in rpms between P and D?

Cheers,

Christian :)


I'm not sure, as my car does not have a tachometer/rev-counter  ::)


There is a difference in revs between P & D, but I'm not sure of the amount.

Jan S

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Re: CO% at idle on 350SE (M116.985) with K-jetronic
« Reply #6 on: 11 April 2021, 02:45 PM »
I have a M100.985 (6.9) and rev is about 850-900 when really warm in P. Rev drops about 100 when in D.

CO at the last test one year ago was 1.55.

I recently replaced the entire fuel assembly, hence I will do a new test the next couple of weeks.
1975-mod W116 450 SE with 6.9 engine