Idle recommendation CO, vacum or??

[mulrik]

When all the other (WRD, valves, venturi, etc) settings are correct What is really the most accurate method to set idle?

The Haynes manual describes the CO to be between 3,5 and 4,5 % at 750-800 RPM.
My BBB says something about adjusting idle to 750-800 RPM and if idle is fluctuating then it's is too rich and if the engine vibrates it is too lean (how is vibration defined....).
Then there's the vacum method that is described in the technical manual on this site.

Which one is preferable if you were free to choose and didn't had to think about availability equipment etc.

Best wishes,
Ulrik

[Larry & Norma]

I bought a Gunsons CO2 exhaust analyser (CO2) which worked a treat. Idle is spot on and runs well.
I could not get the vacuum method to work properly.

[ctaylor738]

I have a Gunsons, so that's the only method I used, works quite well.

[stickandrudderman]

I've been doing it 30 years and have never used vacuum to set idle speed, only to check engine condition/performance.
Here's a rough guide:
Assuming you've connected an accurate tacho and can attain the correct idle speed:
When you turn the idle screw anti-clockwise, you shouldn't get much more than 100rpm increase. If you do then the mixture is too rich and if the idle speed reduces or becomes lumpy then it is too weak.
The idle screw (on the inlet manifold, the one on the pump is the mixture screw) simply introduces more air into the mix; once you understand that it becomes fairly obvious.

[Cees Klumper]

I also use a Gunson's, very happy with it.

Stick is referring to the idle air screw on the intake manifold, not the idle (fuel) adjustment screw on the back of the fuel injection pump. At least I think he is!

[Dahlknudsen]

I just had mine tuned at mercedesbenzservice.dk and the car is runing extremely well now. Call Brian and he might Help you - he speaks Danish so it might be a litle easier to understand...

[stickandrudderman]

I've modified my post fr extra clarity....
If you can't get somewhere near with this method then it's probable that you've got another issue somewhere.

[mulrik]

I have no trouble in doing either of these methods myself. So that's not the problem or my question. I have actually used the CO method twice with good results.

My question was more on a general basis. Which is actually the best method? And then I suggest that we post that method on the technical manual, or perhaps all three.

BR,
Ulrik

[stickandrudderman]

Well, the BEST method to set idle speed and idle mixture is certainly to use a calibrated CO machine, or better still one that monitors hydrocarbons as well as this will indicate any combustion issues you might have.
It's also worth noting that adjusting the CO should be done AFTER making any other adjustments/repairs.