Hello All-

recently inherited my grandmother's W114 1976 280.
My grandma calls her 'The Handsome Old Gal' and with good reason: she is in outstanding shape as far as paint and interior goes. (Seen winters but no salt ) Starts all sorts of conversations, which is super fun, however, she stalls out when I move the automatic transmission gear shift from 'P' (or 'N') to 'D'.

Some background:

Drove her this past winter to the Bay Area from Montana (1500 miles) just fine, although she drank up a quart of oil every tank of gas (~250 miles). It pretty much went away about 1000 miles into the trip and then demanded 1 quart per 4 tanks or so. Didn't see any leaks below, so decided to ignore this ... Was having trouble with cold starts (my grandma did too), but had good MPG, at least 20 (60% highway/ 40% city). Then, the rainy season started, and she began to have trouble sometimes, stalling out in while in D while at a stop or just pulling out from a stop. Took her to a mechanic who turned up the idle. Seemed to help but still stalled out too frequently for my taste. Had the mechanic do a minor rebuild on the Solex (replacing gaskets + the carb mounting flange) after he insisted the carb was the problem. (He did the whole carb cleaner spray test). I got the car home, but just barely. He said he fixed a few vacuum leaks, yada yada, but now the car will only drive if the idle is turned WAY up. Said there was something wrong/leaking with the fuel pump vacuum or something but I was little inclined to believe him.

After reading around on these boards, I figured something I could first off do myself was change the plugs and wires. My grandpa insisted this is important, as bad plugs on this car once caused him a big headache. Pulled the old plugs, saw they were in bad shape, changed them out, turned the idle speed on the carb down to something that sounds nicer, and got some improvement with idling. The engine sounds smooth (with a tiny bit of 'puff'-ing occasionally), and the car drops down from the high cold idle to the warmed-up lower idle, but it immediately conks out when I shift into D. The funny thing is, the battery, which never gave me troubles before, now will not start the car...

So, the cold start problem is gone. Yay.
The car starts right away with a jump.
Idles just fine, no smoking out the back or leak-spots beneath.
Really Wants to keep running in Drive, but can't, and then won't restart w/o a jump.

Any suggestions of what I should do?
Does this sound like a timing problem?
A Carb problem?
An electrical problem?
A transmission problem?

I am more determined to fix this myself if I can, rather than pay someone else to make the car run even worse...Or a least have some idea from people who really know and care about these old cars before I venture out onto the 'mechanic market' again. ( I'm a student in the Bay Area, and mechanics around here want $100/hour at independent shops (!))

What do you all think?
Many Thanks-

CJ

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1976 W114/M110 280
"The Handsome Old Gal"

I am more determined to fix this myself if I can, rather than pay someone else to make the car run even worse...Or a least have some idea from people who really know and care about these old cars before I venture out onto the 'mechanic market' again. ( I'm a student in the Bay Area, and mechanics around here want $100/hour at independent shops (!))

What do you all think?
Many Thanks-

CJ[/QUOTE]I know about but don't really care for those older cars, but I will offer some help. First off it was a mistake to let that mechanic rebuild that quadro jet. It is not the same as an American quadro jet. He probably cranked down on the four corner bolts which distorted the air horn and will now cause trouble with the secondaries. What's done is done. I would suggest a valve adjust if grandpa didn't want to spring for the expense. It should be done every 15,000 miles. Secondly I would set up the dash pot to factory specs. It is supposed to advance the idle when in gear or A/C is turned. Next I would be sure the vacuum box that sets pre throttle gap is functioning properly and also make sure the the pre thottle gap openning is correct. Keep me posted.

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Auto Zentral Ltd.

One thing to check is whether the idle valves are working.

You will see two conncectors at the base of the carb. With the igition off, loosen the connectors so you can pull them off easily, but leave them attached. Turn the ignition on, and unplug and re-plug each connector. Each time you do this, you should hear a "click." If you don't, then the valve is bad and needs to be replaced.

These valves are open when the ignition is on, closed when off. Their function is to stop fumes from escaping when the engine is off. If they don't open, the idle circuit does not get any gas.

The problem you are facing is that these carbs did not work very well even when they were new, and they are very difficult to repair as they age. They develop vacuum leaks from heat and over-tightenting and wear around the shaft bushings. With a 1976 car, you have the latest and best of the 4A1's but it is also in the middle of the most complicated emissions system, which has all sorts of pieces that can cause problems. You could well have a switch or relay failing causing the hot idle problem.

If you are going to try to troubleshoot, get a copy of the "Service Manual Engine M110" from Mercedes or eBay, which has great detail about the carb and its surrounding systems.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Chuck,
Good point. I forgot about the idle shut off valves. It has been years since I've woprked on one of these carbs. Also the o rings on the idle jets must be in good shape or they will cause idle prooblems. I always lubed them with silicone paste. Buying that carb, the Ford cruise control, and the Chrysler climate control were MBs biggest boon doggles.

I may have an extra copy of the manual I can sell. I'll have to check.

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Auto Zentral Ltd.

You may have to adjust the vacuum idle regulator (driver side of carb).
Unplug the hose and set the idle to 2000rpm (at lot) with the bold on the end.
Then reattach the hose and adjust the spring tension with the big nut.
With an automatic transmission there should be a 1mm between he bold and the linkage, if you have an airco, switch it on and adjust the spring until the car idles well.

An other thing to look at is the ignition. Set the points to 39-41 degrees, this is very important. One degree off and the car will not run as it should.

Maybe.

But the car should idle in P or N at about 800-900 and drop to 650-750 in gear without the vacuum assist. It is supposed to give a boost when the AC is turned on or the power steering is engaged at low RPM.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe