Hi All,

I have a 1979 300TD Automatic, NA. What is this vacuum diaphram thing on top of my IP? (Big Saucer thingie). It looks like an ALDA found on Turbos but my car is NA. I checked the number on the pump and it is the right one for the 79 300TD. There appears to be a fitting to it that isn't hooked up.

1) What is it?
2) What does it do?
3) How do you set the screw adjustment (appears to affect mixture)?
4) What should it be hooked to? (vacuum pump, manifold?)


I have tweeked the screw a few turns in both directions and it appears to make my horrible smoking problem go away but along with the neck snapping power . (Smoking Saga thread). The screw looks like a preload for some kind of vacuum diaphram.

I've looked around in the online CDs and Haynes and cannot get a clear idea. Any help would be appreciated.

Cheers,
Yoko

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That device is kinda like a half of an ALDA, it serves to altitude compensate the IP. It will try to keep the IP from over fueling the engine when you travel to high altitude locations. Can not help you on the adjustment question, but I believe it is only supposed to be hooked to the atmosphere, ie. no hook-up at all.

__________________
1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Yes this is an ALDA and turning the scewdrive head CCW will enrichen your takeoff fuel ie lots of smoke if you are much above sea level. If you are at sea level it is already as rich as it can get by design.

__________________
1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C

Hi,

Thank you for the 411. I do notice when I turn it in CW, it seems to get leaner at idle and the takeoff is very weak. I turn it CCW and it gets smokier and more powerful at takeoff as you say.

I think it is supposed to have no hookup. I put the output side of my vacuum pump on it (blow) and pumped it while starting from stop signs and it definitely launched much better.

So this all adds up. High altitude is thin air and you need to lean out so this is consistent. Low altitude means more pressure then that means more fuel for the more dense air. Okay, I think I get it, but I was hoping it had some kind of hookup that would blow in it during takeoff.

I'm fighting with this smoking problem at idle and this is consistent with the smoking. On startup idle there is little smoke at warmup but once warm the smoke starts. It has me wishing I could lean the idle. Makes me wonder if there is some kind of compensating mechanism that is failing at temp? Hard to say. Right now I'm living with the power loss so I don't embarrass myself in traffic. I'm going to start casually searching for a takeoff IP in the yards.

Thank you for the inputs.

Cheers,
Yoko