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Garage => Mechanicals => Topic started by: Berggreen on 11 April 2021, 06:03 AM

Title: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Berggreen on 11 April 2021, 06:03 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
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: ptashek on 11 April 2021, 06:18 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.
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Type17 on 11 April 2021, 01:07 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.
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Berggreen on 11 April 2021, 02:03 PM
Quote from: Type17 on 11 April 2021, 01:07 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 :)
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Berggreen on 11 April 2021, 02:05 PM
Quote from: ptashek on 11 April 2021, 06:18 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.

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

Cheers,

Christian
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Type17 on 11 April 2021, 02:11 PM
Quote from: Berggreen on 11 April 2021, 02:03 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.
Title: Re: CO% at idle on 350SE (M116.985) with K-jetronic
Post by: Jan S on 11 April 2021, 04:45 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.