fuel mixture test

[Peter]

I want to test the fuel mixture as describted in the Haynes Repair Manual.

Still some questions for the ones who have experience with this test.
1. The crub screw will be moved from position 1 to 2 (see picture). Wil the hole of position 1 be closed (with e.g. a screw)?
2. The vacuumhose, now connected in location 2 is on the otheside open? See point 3 in the text (section 28)

Thanks for information, Peter

[Nicolas Aristodemou]

Peter if you are trying to adjust the fuel/air mixture I think your best best bet would be to follow the linkage tour procedure as described in the technical manual found in this site.

Your adjustments should be the idle mixture screw on the fuel injection pump - move one click at a time with the engine switched off - and the idle air screw (big slotted screw on the intake manifold next to the throttle body. You are basically trying to set an idle speed of 750-850rpm using the slotted air screw on the manifold and make sure that this is about the maximum rpm you can get and that opening the air screw further decreases rpm. If rpm still increases past 800 rpm when opening the slotted air screw then your mixture is rich and you should close the idle screw mixture on the FIP by a click and try again till you get 800rpm as your maximum idle speed before further opening of the air screw no longer results to rpm  increase but to decrease. Likewise, if you cannot get to 800 rpm by opening the air screw then your mixture is lean and you should enrich it by a click at a time -engine off- till you achieve your maximum rpm at around 800. You can also connect a vacuum gauge on on of the engine vacuum tap offs using a T fitting and observe your readings idle. Maximum rpm should be also maximum vacuum at idle (between 17-21 inches of vacuum). Turning the FIP knurled know clockwise makes the mixture rich and counter clockwise lean.

I went through the Haynes manual procedure (section 28) but really do not understand what is the object of that exercise and how it is achieved.

[Peter]

I went through the Haynes manual procedure (section 28) but really do not understand what is the object of that exercise and how it is achieved.

Nicolas,

I also wondered how this procedure comes to a conclusion. So back to the good old linkage tour procedure.

Peter

[mrfatboy]

Also make sure the engine is 100% at operating temperature before doing the adjustments.  Sometimes it’s wise to take the car for a quick spin around the block to get it there. Once you get your mixture correct at operating temperature then concentrate on the WRD (warm up mixture).

[Peter]

Thanks, I was just in the process of follow your suggestion.

• Linkage
• Run the car to 180 F
• Altitude Compensator (+ 0,5 mm – a bit richer), car is stalling when cold since I decreased (- 1,5 mm,
  bacause it was much to rich)
• Ignition timing (6 – 8 BTDC - with 123)
• CO measurement to +/- 4,5 – 5% at idle
• WRD

Peter

[mrfatboy]

It would be helpful  to know the following info:

What is your year and model of your car?

What is the model of your FIP?

What is the current thickness of your shims under the BC (or AC)?

You say your car was stalling when cold. But if you were to keep it from not stalling and getting it to operating temperature did it want to stall anymore?

[Peter]

Model:    280 SL USA version early 1969
FIP:    PES 6 KL 70B120 R20Y

Engine started stalling when cold (shifting from R to N to 4 and back) after I decrease the number of shims from the Altitude Compensator because the car was running too rich. No stalling when warm.

Actions today:
• Linkage: checked and ok
• Altitude Compensator+ 0,2 mm from 1,9 to 2,1 mm
• Ignition timing: ok at 6 BTDC - with 123)
• CO measurement 5,9 % at 750, can’t get it lower to the 3,5 -4,5% as it should be.
 
Engine is running very good.

Tomorrow when cold the stalling test.

Peter

[Nicolas Aristodemou]

Peter don’t worry if your CO is little bit high compared to specs. These engines are happier running a little bit rich.

Also does Your car have the vacuum pot under the throttle body to control the idle when shifting from N to 4 ot R?

If it does make sure it is adjusted correctly. I think the Haynes manual gives good guidance as to how to adjust that. It’s main function is to prevent the engine from stalling by opening the throttle a little bit with the aid of engine vacuum.

[mrfatboy]

@Peter,
 
You have the same FIP I do.  The BC (AC) came with a 2mm shim washer from the factory. You are very close.  Adjusting the BC adjusts the mixture at all ranges and temperatures.  If it were me I would set it back to 2mm.  That way you know it is factory set(That's assuming nobody has messed with anything inside).  Then use the FIP idle thumb screw and the idle air screw on the manifold to adjust your Hot running idle and CO.  Once you get that they way you want it it's time to play with the WRD shims, etc to get your cold idle working smoothly.

The steps I would take:

1) Set BC shim to 2mm
2) Get Car to operating temperature
3) Measure CO
4) Start with adjusting the idle air screw on the manifold to lower CO and get nice idle.
5) If CO too high, turn off engine, turn FIP thumb screw CC 1 click to lean pump. If CO too low, turn engine off, turn FIP thumb screw clockwise 1 click.
6) Start engine and go back to step 4 until you get desired setting.

Now let engine get cold and test warm up idle and CO.

1) Start engine and let warm up
2) If the engine dies because it's too rich, reduce thickness of oval shims under wrd.
3) if the engine dies about 3-5 minutes into warm up it's probably getting too lean during the "lean period" of the warm up cycle. If so you can back off the two screws that hold the WRD to the FIP slightly. This will simulate enriching the warmup cycle.  Once you get a complete warm up cycle without the engine stalling you then can put the correct oval shim thickness under the WRD.

You can check out FIPi in the tech manual to see a normal CO warm up curve.  If you really want to dial in the CO you can map your on CO curve and see how it compares and make more minor adjustments.

https://www.sl113.org/fip/index.html

Also, I have found once you start adjusting the FIP thumb screw it takes time to "settle in" the adjustment.  You will find that after driving 10 miles or so and you remeasure the CO it probably will change and minor adjustments will need to be made.  This is normal.

Of course, the above advice is worthless if the linkage, CSS, etc is not adjusted properly 

Good Luck!

[Peter]

Thanks for good advise.

I was not aware that the factory adjustment was 2 mm. I will bring it to 2 mm and adjust if needed the CO/idle, see how it runs and how the spark plugs will look like after a few 100 miles.
Then I will concentrate, if needed, on de WRD. Could well be that the stalling is solved with the extra 0,1 mm (from 1,9 to  2,0 mm).

Peter

PS: the linkage is perfect!