Increased RPMs at warm-up?

[Berggreen]

Hello all

Over the recent time, I have been noticing how other Pagodas, and especially the 280SL, behave during warm-up. I see that most warm up at increased RPMs at around 1200 RPM which then gradually reduces and returns to the standard 800 RPM, as the warm running device (WRD) returns the increased mixture to the base idle mixture, when the coolant reaches the operating temperature. 

But both my 280SLs (1970 manual and 1971 automatic and both with R24Y injection pumps - FIP) do not do that! They both cold start fine, but they warm up at around 600-800 RPM, and can at times struggle to stay running, especially towards the end of the warm up phase, and especially if I try to decrease the warm idle mixture.

However, my warm idle mixture should be about right on both of them, and I have just changed both the WRD thermostat and small air-filter on both of them, but without any effect.

So my questions are:

1) Should all 280SLs, no matter which FIP they have, be warming up at increased RPMs, or do the very late FIPs like the R24Y not do that?

2) If they should indeed warm up at increased RPMs, what is then the typical problem if they don't, and instead behave like my two 280SLs? 

Hope you can help with some input to guide me in the right direction. 

Thanx,

Christian 

[stickandrudderman]

The simple test is to remove the auxiliary air filter when engine is cold, start the engine and observe whether there is vacuum at the air filter port. You will hear it. There should be a lot of vacuum and associated noise when cold and it should decrease to virtually nothing (a little bleed is OK) when the engine is hot.
If there's no vacuum, or very little, when cold then your WRD is not functioning and in all likelihood the mixture has been adjusted to compensate.

[Berggreen]

The simple test is to remove the auxiliary air filter when engine is cold, start the engine and observe whether there is vacuum at the air filter port. You will hear it. There should be a lot of vacuum and associated noise when cold and it should decrease to virtually nothing (a little bleed is OK) when the engine is hot.
If there's no vacuum, or very little, when cold then your WRD is not functioning and in all likelihood the mixture has been adjusted to compensate.

Thanks, and I had the same thought and plan, and will try to do as you propose.

But the fact that both my 280SLs with R24Y FIPs are behaving in exactly the same way, and that I saw no difference, when I changed the WRD thermostat and filter on both of them, my thought was that maybe these late 280SL FIPs have some feature which removed the increased RPM function at warm-up.

[Berggreen]

Follow-up:

I just checked the function of the WRD and removed the small air-filter, and there is plenty of vacuum and air being sucked at cold start, and no vacuum with warm engine. So it seems the WRD is operating correctly.

Cheers,

Christian

[Berggreen]

Hi All

I am very interested to hear from other 280SL owners, especially with a R24Y FIP (fuel injection pump).

Do you see increased idle RPMs at warm up, or does the idle stay at approx. the same as with a warm engine?

Also interested to hear from other 280SL owners with a late FIP, like R23 and R25.

Looking forward to hear from you.

Thanx,

Christian

[Pawel66]

With R25 I have increase to 1100 -1200 rpm initially, going down to ca 850 between 70-80 degrees.

[Peter]

With R25 I have increase to 1100 -1200 rpm initially, going down to ca 850 between 70-80 degrees.

My WRD is functioning correctly in timing/length, it closes at 70/80 degrees C. But maximum rpm is around 950/1000.
My understanding is that adding a shim will increase the length (is degrees) which is not necessary.
Question is how to increase the rpm without increasing the length?

Thanks Peter

[Pawel66]

I guess you would have to check ignition timing (8 BTDC at idle) on enrich the fuel (oval shims). Why would you want/need to have higher rpms? I am not sure if it is necessary.

[JamesL]

Odd thread as I noticed the other day that when warm I idle at about 1400 in neutral but about 850 in drive. Wondered if the former was normal, though it seems the latter is

[Peter]

Ignition timing, CO, altitude compensator, all perfect!
But when I start car and put it in revers or 2 is stalls.
This only happens the first 2/3 minutes then this is not happening any more.
So, my idee was increase rpm during warming up, which is now 950/1000, which seems to be low.

Peter

[bracurrie]

On My 1970 M130 USA specs w R24Y FIP when the speed switch was operating and the ignition timing retard was working properly the engine at cold startup would cancel the normal timing retard at idle thus it would idle approximately 1000 RPM until enough temperature would put the retard back in and the car would then idle approximately 800 RPM. But then my speed switch went wonky so I disabled the retard and reset idle mixture to get 800 RPM at idle. Now when I start the engine cold idle is too low, but because I have a manual its not a problem.

[Berggreen]

On My 1970 M130 USA specs w R24Y FIP when the speed switch was operating and the ignition timing retard was working properly the engine at cold startup would cancel the normal timing retard at idle thus it would idle approximately 1000 RPM until enough temperature would put the retard back in and the car would then idle approximately 800 RPM. But then my speed switch went wonky so I disabled the retard and reset idle mixture to get 800 RPM at idle. Now when I start the engine cold idle is too low, but because I have a manual its not a problem.

Thanks for sharing your story, because that makes a lot of sense to me too! Because my cars are also original US cars, where all the speed switch and the rest of the US emission control system has been disabled years ago. Now both cars are tuned like a European 280SL and with 123ignition systems (warm idle 800 rpm and 8 degrees BTDC).

But I have not yet changed any settings in the warm-runnng-device (WRD), and therefore it is still working, as if the US emission control system is still there to cancel the ignition retard at low temperatures.

So in order for the WRD to operate like in a European 280SL, I suspect we need to regulate the fuel/air mixture with the oval shims under the WRD to get the cold start idle up to around 1000-1200 rpm. Secondly, we may need to extend the warm-up period as well with the round shims inside the WRD - but I guess, we should start with the oval shims to get the 1000-1200 rpm idle immediately after the cold start.

Does that make sense, or am I on the wrong track here?

If not, and to have a good start point, does anyone know how many mm of oval shims the European 280SL has under the WRD as standard?

Cheers,

Christian

[bracurrie]

When you installed your 123 Ignition distributor, did you move your vacuum source to drive the dizzy to retard when under light throttle or deceleration like the 051 Bosch dizzy?

I am asking to have a R24Y FIP rebuilt using a three dimensional cam from an R20Y and the fueling specs from an R20Y for calibratiion.  The R20Y was on the 1968-69 M130.980 engines which were the last ones before US emissions regulations forced MB to lean the fueling in the lower load ranges. The rebuilder is curious and promised to share the fueling specs for both the R24Y and R20Y so we can see the difference. Idle mixture would have to be close to identical for both but since I don't have any experience with a CO measuring tool I don't know happens when you set idle to CO specs versus balancing the idle mixture. My suspicion is that if you ran it to the rich side the engine may do better at cold idle if your warm/hot idle speed is 750-800 RPM. For me having resolved a rusty tank issue my engine is behaving better every tank.  It will almost stay running at idle when started cold. It runs for 5 seconds then dies.  Re-starts at idle and stays running.  I cannot rule out that someone may have monkeyed around with the FIP and at 50 years old the rebuilt FIP may improve cold start and inconsistent warm to hot idle running. There may be some other considerations for automatics that I don't have to worry with. 
I believe I have seen in this forum where the 123 Ignition dizzy where you can control the advance curve in software it may be possible to program in additional advance at startup which could improve cold and hot start. As many will attest, hot starts can be a problem for these M130.980 engines.