WARNING! : DO NOT START WORKING ON YOUR FIP BEFORE YOU ACHIEVE THE BASIC SETUP FOR YOUR ENGINE : CORRECT VALVE CLEARANCE AND IGNITION TIMING AND LINKAGE SETUP !! THIS CANNOT BE STRESSED ENOUGH , OTHERWISE YOU ARE TRYING TO SOLVE ONE PROBLEM BY CREATING ANOTHER ,WHICH WILL DRIVE YOU CRAZY IN THE END ! !.
230SL bad engine running/starting mini tour Part 1 : the basics (
https://www.sl113.org/forums/index.php?topic=38391.msg280468#msg280468 )
230SL bad engine running/starting mini tour Part 2 : Air and Fuel supply (
https://www.sl113.org/forums/index.php?topic=38392.0 )
230SL bad engine running /starting mini tour Part 3 : CSV , injectors and checkvalves (
https://www.sl113.org/forums/index.php?topic=38428.0 )
FIP ( R11)
Basic mixture control : it's all about the "rack" ! !
This is only a limited explanation just to give some useful background info for the average SL owner. I try to keep it simple...
You may remember from Part 2 , that air and fuel need to be in a certain optimum ratio ,theoretically a 14.7 : 1 ratio ,so throttle body (air) and FIP (fuel) need to operate in sync.,achieved by a correct linkage setup to begin with.( see Part 1 : the basics).
Pressing the accelerator pedal you directly control ,via various levers. the throttleplate angle in the throttle body . So a kind of "hard" link .This throttleplate angle dictates the (size of the) opening in the venturi and thus the amount of air entering the inlet manifold.
Via the main linkage system the FIP lever (angle) is controlled in sync. to add fuel. The simplified basic idea is that a given throttleplateangle corresponds with a certain amount of fuel from the FIP to obtain the right air -to-fuel ratio,the AFR .This FIP lever angle is just one of the inputs that controls the rack movement inside the FIP .
Now what is the hack is the rack? Well, the rack ,in turn, controls the amount of fuel delivered by the pumpelements .
Confused already ? Look at this excellent video that I found which explains the principle of how the "rack" and "pumpelements" determine the amount of fuel. A "must see" for a better understanding.
https://www.youtube.com/watch?v=eA5qipliN9wBy now that you may understand why the fuel amount of the AF mixture is ONLY directly controlled by rack position..(exeption : fuel injected by CSV at engine start )
Rack postion ,however, is determined by several inputs:
a. throttle lever angle
b. BC, the barometric compensator
c. WRD,warm running device
d. starting magnet for enrichment at the rear of FIP
e. idle thumbscrew up to about 1700 rpm via the ( not discussed here),cam/governor assembly with its white and black partial/full load screws.
f. the internal rack adjustment screw
WARNING :Before talking about adjustments DO NOT make ANY adjustments at the throttle lever stop or the black and white screws for partial/full load ! ! !
Mixture adjustments.
For a quick check to determine if your mixture is more or less correct you can do the split linkage test ,
or my favorite way : the ease of use of the Colortune is the most convenient way to observe the mixture at any rpm without fumbling with levers.How the Colortune works is earlier explained in Parts 1 and 2
Fine tuning can be done later using a CO-meter
First a little bit of explanation of the internals of the FIP. (see attached drawing)
As earlier said ,the rack position is amongst others influenced by the pin lenght of the WRD and BC .These pins are colored light blue in the drawing.
Keep in mind that lever C directly controls the rack position,thus amount of fuel.. The interconnection between them is for simplicity not shown in the diagram !.
In a
stable ambient/atmospheric pressure condition the BC pin has a certain fixed length, presses on lever A and acts then as a static "pivot point"
When atmospheric/ambient pressure decreases ( i.e driving UP in the mountains) the BC pin extends further, pushing down on levers A,B and C. At higher mountain elevations air pressure is lower and less fuel is needed to keep the AFR in balance. The opposite holds true as well : an increase in ambient pressure raises levers A,B and C due to a shorter BC pin lenght..
The WRD has a similar effect.
When your engine is warming up after a cold start the WRD pin extends more and more and exerts an increasing force on lever A,B and C , resulting in leaning your mixture as (coolant) temperature rises.
https://www.sl113.org/forums/index.php?topic=11928.msg80307#msg80307 (Photo with FIP internal levers)
If a mixture adjustment is necessary , your first step should be making adjustments effecting the FULL rpm range, (start working on idle mixture and coldstart phase mixture later)
The easiest way this can be done ,on a warmed up engine, is by means of shims UNDER the BC( round shims),WRD ( oval shims).
A good advice from the Benz dr. when shimming the BC :
https://www.sl113.org/forums/index.php?topic=30847.msg223874#msg223874Simple rule of thumb to keep in mind :
ADDING shims means ADDING fuel so your mixture gets richer.
REMOVING shims means REMOVING fuel so your mixture gets leaner.
Note 1: when using the same thickness,adding or removing round shims under the BC has greater impact on mixture than oval shims under the WRD.
Note 2: after each mixture adjustment drive the car a couple of miles to let them "settle" and stabilize under load and temperature. Recheck afterwards.
Note 3: If you're trying to lean a (still) rich running engine and all shims under the BC have been removed already , you may have to go a step futher and adjust the internal full range rack screw.
Do this only in small increments i.e. 1/4 of a turn ,it is very effective !
Remember this : turning the rackscrew clockwise (CW) will LEAN your mixture and turning it counterclockwise (CCW) will RICHEN you mixture !! https://www.sl113.org/forums/index.php?topic=36878.msg279593#msg279593 ( adjusting the rack screw)
After setting up your full rpm range mixture now you can adjust your idle and lower rpm mixture till appr. 1700 rpm.
First determine if your idle mixture is lean or rich by either the split linkage test or using the Colortune.
I assume you know how to handle the thumbscrew.
Then adjust your idle mixture by using the large airscrew on the manifold and the thumbscrew on the back of the FIP to obtain a smooth idle at 750-800 rpm
https://www.sl113.org/wiki/Restricted/Linkage-tour#Idle (the idle adjstment paragraph)
https://www.youtube.com/watch?v=F6sxlOFmoYw. ( 46 min. idle adjustment video ,long but nice procedure)
I personally prefer the Colortune which makes mixture adjustments a piece of cake and takes only minutes and resulted in a very satisfactory running engine.I kept it there, good is good enough.
The purists among us can try to achieve the published factory CO setting .( no offence)
* BC : simple functional check and problems
It's important for those measuring the pin length of their BC to do so from the base of the hex nut to the tip of the pin. A good BC should measure approx 21mm. A bad BC will measure approx 25-26 mm
An other simple functional BC check and other helpfull hints can be found in one of my earlier posts :
https://www.sl113.org/forums/index.php?topic=35141.msg256971#msg256971 A BC failure often results in a very LEAN mixture , the pin sticks out quite a lot and thus changing the rack position excessively.
https://www.sl113.org/forums/index.php?topic=30847.msg223874#msg223874 ( BC failure topic with nice pictures)
If you observe anything incorrect in my text please PM me so I can adjust it.
To be continued...
