Author Topic: Idle fuel/air adjustment (Read 12403 times)

col320ce · « **Reply #50 on:** May 06, 2020, 00:22:18 »

That's exactly what I needed to know MrFatBoy. I was thinking that a cool running car is also a good thing too!

I still have not measured the fuel flow. Is it recommended to use a flow meter for this or simply disconnect the fuel line and collect the fuel over a specified time? Is this done at the return hose near the fuel pump?

Thanks

mrfatboy · « **Reply #51 on:** May 06, 2020, 00:45:25 »

I have attached a chart of CO% over time during warm up.

This data has been collected from multiple 250's and 280's local here in San Diego. We use it for tuning and overall understanding what the heck is going on with the FIP😄. As you can see from the chart some cars were running lean or rich and then tuned correctly.

The take aways are:

- You want the overall curve shape in the graph. The curve shape can compress/extend, shift down/up depending on factors when you start taking the next tuning steps.

- Notice the low dip on chart toward the end? Thats the time that the airslide valve is still slightly open for that lean period I was taking about in the last post.

Regarding fuel flow, I believe it's ~1 liters in 15 seconds? Someone please check my memory🤣

When I did the test I did it right before FIP. I think I just read a couple of weeks ago (again check my memory 😄) it was also good to test flow at the return line to the tank.

More tests/info can never hurt😄

col320ce · « **Reply #52 on:** May 06, 2020, 03:27:04 »

Now that graph makes sense ... I saw it before and didn't really get it. I do have an old Bosch CompacTest (MOT 350 with the CO/CO2/HC analyser and MOT 401)... No idea how to use it but I'll do some research tonight. I'm sure it will help get the old girl purring again.

Pawel66 · « **Reply #53 on:** May 06, 2020, 06:32:51 »

Quote from: col320ce on May 06, 2020, 00:22:18

That's exactly what I needed to know MrFatBoy. I was thinking that a cool running car is also a good thing too!

I still have not measured the fuel flow. Is it recommended to use a flow meter for this or simply disconnect the fuel line and collect the fuel over a specified time? Is this done at the return hose near the fuel pump?

Thanks

I think the simplest recommended test is to measure flow at the end of return line. Up to a litre in 15 seconds. Let the fuel pump warm up a bit. If you are 0.6-0.7l - it is already a low flow.

col320ce · « **Reply #54 on:** May 06, 2020, 06:39:22 »

Hi Pawel
Are you just running it into a container or do you have a flow meter set up?
Thanks!

Pawel66 · « **Reply #55 on:** May 06, 2020, 06:59:47 »

Just to container. Since I am not a mechanic, I do not even have this kind of tools.

I did this test when I was looking for clogged spot in my fuel delivery system. End of return line is giving full picture and is easy to access even for weekend mechanic like me - either the tank or at the T connector (late cars) if you have it.

col320ce · « **Reply #56 on:** May 25, 2020, 10:41:40 »

I've finally got the air shutting off through the WRD ... and the car stalls. I assume that the WRD has not been set properly for years as it had only 0.2mm of shims in there and that's not even enough for a new thermostat to turn off ... so I also assume this car has been "tuned" in the warm up state and as I mentioned before it blows loads of petrol smoke.
I can keep it going if I press on the throttle but it dies as soon as I release it making it a little hard to do the split linkage test.
Is there a starting point of the BC and a number of clicks that I should be counting on the FIP (eg 20 clicks back from all the way in) and go from there? I've got the BC loose and I'm still struggling to find a position for it to keep the idle going when warm.
Or is there a technique?!
Thanks!!

wwheeler · « **Reply #57 on:** May 25, 2020, 15:53:01 »

I have a total of .080" worth of shims under my BC if that helps. Maybe that is a good starting point? You can use a rubber hose and jam it between the BC and the WRD to keep the BC from turning during a test drive.

Is it possible the idle speed is set too low (too little fuel and air) when the WRD air shuts off? If the WRD was previously sucking air, that means that it was also injecting more fuel. The two happen jointly and that ratio cannot be changed. More fuel and more air translate into a higher idle speed.

Pawel66 · « **Reply #58 on:** May 25, 2020, 16:55:58 »

So the engine runs when warming up and when warmed up it dies if you do not press the linkage? And it is producing lots of smoke when working? That would suggest it is too rich.

You can also split the linkage, keep it down holding both levers together by hand and with the other hand press or release one of them.

How much of shims do you have under the BC? More than what Wallace is saying? If yes - it is rich.

I started from 2mm of shims under the BC - it was advised to supposedly be close to starting point. It worked for me.

stickandrudderman · « **Reply #59 on:** May 25, 2020, 18:05:59 »

It is possible to crank the car with the key and operate the throttle linkage directly with your foot by cocking your leg over the wing (fender)! This gets you enough RPM to quickly change from foot to hand and so keep it running while you make adjustments!

Pawel66 · « **Reply #60 on:** May 25, 2020, 18:11:42 »

Could you make and post a short film to show us how to do that?

mrfatboy · « **Reply #61 on:** May 25, 2020, 18:12:05 »

Here is an old post how to set up remote starter

https://www.sl113.org/forums/index.php?topic=16067.0

Pawel66 · « **Reply #62 on:** May 25, 2020, 18:19:44 »

If you do not have automatic, you can use pin 86 in cold start relay and an impulse switch. So: run the wire from + on battery (I did it with the fuse) to the impulse switch and from switch to pin 86 on cold start relay. Ignition on and engine will crank when you press the switch. Stop cranking when release the switch. Switch must be impulse one - connects only when you hold it, does not stay switched on when released.

col320ce · « **Reply #63 on:** May 26, 2020, 08:54:02 »

Today was a good day. The car is running really well but I feel that you might tell me that it will still be too rich.
I started by getting the car warm which was an effort in itself ... basically getting a mixture that allowed me to drive the car (it was stalling whenever I took my food off the accelerator.
I then adjusted the BC so that at higher revs the split linkage test was "normal".
Then adjusted the FIP thumbscrew for idle.
It's now idling at 800 ish. It's a little lower when its not fully warm but I don't know what it will be like after a full cool down over night. If it's idling too low during warm-up I'll add an oval shim to the WRD.
The car occasionally stalls when I stop quickly ... which I think I adjust the linkage dampener dashpot to get right?
The car drives beautifully and I don't think has run this way in many years. My only concern is that the BC has got 5mm of shims under it and this is way off the starting point of 2mm. But it's also the wrong FIP for the car (it's one for a 250SL) so this may account for that.
I'll get it all more accurate when I get the Bosch CompacTest up and running (currently translating the German instructions into English).
I'm taking it for a couple of hour drive tonight so I'll see what the plugs look like after this ...

BTW my technique for starting the car is window down, reach in and start the car and use a 1x1 inch block of wood on the venturi rod. Works well but I sometimes lose it when I swap to the other side of the car. Probably not as easy on a LHD car ...

ronwall83 · « **Reply #64 on:** November 03, 2024, 22:40:11 »

Really old thread, so here's hoping...

How do you turn/remove the compensator? My car is a '66 230sl and runs far too rich. I think I can feel shims underneath, so if I want it to lean up a bit then I need to remove a shim or two... am I reading that right?

wwheeler · « **Reply #65 on:** November 04, 2024, 03:43:45 »

Under the round can, there is a hex for a wrench. I can't remember what size but maybe 19mm? Use that to loosen the can.

You say far too rich. What engine RPMs is that at? The compensator will more or less adjust the mixture at all rpm ranges. You first need to determine at what RPMs it is rich. If just at idle, It is possible to adjust the mixture at idle alone. But what ever you do, always make notes for what changes you do so you can always go back to where you were.

Yes, remove BC shims to lean. But be advised this adjustment is VERY sensitive. .003" shims can make a significant difference. Ultimately, this is more of a temporary fix. You should change the setting screws in the pump to be proper. But because that can be a daunting task and not for the faint of heart, most stick with the BC adjustment.

ja17 · « **Reply #66 on:** November 05, 2024, 05:10:16 »

The early compensators were 19mm the later are 22mm. The shims are 14mm I.D.

rosch · « **Reply #67 on:** November 10, 2024, 18:21:07 »

Idle /mixture /ignition problems can be easyly identified with a so called "Gunson Colortune". Just Google for it or watch some available Youtube video's.
In short : It is a kind of transparent sparkplug replacement which makes it possible to peer into a cylinder with a running engine and observe the sparking and the combustion process . The color of the combustion process ( hence the name "Colortune") gives you a lot of information wheather your engine is running rich or lean in realtime conditions.
It makes fuel/air adjustments a piece of cake and avoids fumbling with split linkages at especially higher rpm's .
It helped me troubleshooting my poor running engine and is now one of my favorite tuning tools.
Our engines have 14 mm size sparkplugs. keep that in mind before ordering.
I am not a vendor , just regard it as a tip !

Bshaunessy · « **Reply #68 on:** November 10, 2024, 23:13:53 »

ROSCH
Great tip RE GUNSON Colortune spark plug tool. I have found this tool on Amazon.com….14mm plug size. My car is in a different country right now so I can’t measure . Q? What size are our plugs pls? (1970 280 SL). I’d like to order so this tool is there when I get home to my car.

rosch · « **Reply #69 on:** November 11, 2024, 07:17:47 »

Our engines have sparkplugs with 14 mm thread.

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Author Topic: Idle fuel/air adjustment (Read 12403 times)