That fuel cut-off solenoid on the bottom of your carbs' main jet would be my most likely suspect.
It's supposed to cut off fuel when a warm engine is turned off, to prevent run-on or 'dieseling'. Sounds like you're running OK on the cold-start system until it's warmed up. Maybe the solenoid sticks closed when you turn the key off, or its' wiring/circuit is faulty.

Happy Motoring, Mark

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DrDKW

Thanks, Mark. However, I have a spare solenoid that I know works for sure and it still did the same when we replaced it. The only other thing that I can think of is the fuel pump, but the mechanic said he tested it and it seems to be providing enough fuel to the carb.

Aaron Rochard

1976 230. 4 W115

Yes, but I also mentioned the circuit or wiring. If, because of a fault in the electrical circuit or wiring, the solenoid doesn't get power, it won't work anyway.

Other possibilities include the rubber isolator mount between the carb and intake manifold. It can crack, causing a major vacuum leak.(but I would assume that it was checked or replaced during the carb overhaul).

The main carburetor jet could be adjusted way too lean. Once it warms up and comes off the cold-start/enrichment system, it could be starving for fuel. The main carburetor jet is what that fuel cut-off solenoid is attached to. You loosen a locknut and rotate the whole jet/solenoid assy. to change the fuel mixture.

You might need to go back and re-check the basics. Check for possible water in the gas causing frozen fuel lines. Have you tried some gas-line antifreeze?

How experienced is your mechanic with Stromberg carbs? Has he given up? Adjusting the 'Choke' (cold-start valve) won't fix a problem elsewhere in the carb.

Good Luck and Happy Motoring, Mark

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DrDKW

Thanks again, Mark. I'll have the mechanic check that the solenoid is getting power.

As you said, the main gasket should have been done when the carb was re-built, but I'm still concerned with maybe the needle possibly being worn. I have full confidence in my mechanic's knowledge of the Stromberg, because I threw him some test questions and he seems on the ball. He was a Mercedes shop mechanic for 20+ years before he went out on his own. He suspects that it is choke related and will contact the re-builders if he's still stumped after a day or two.

I'll keep you posted,

AARON ROCHARD

1976 230.4 W115

Looks like my car is back on the road and working again. It seems that the start up problem was due to the solenoid sticking after I shut off the engine. The mechanic unplugged the solenoid and re-set the mixture, and I drove to work for the first time in a month !!!

I suppose the carb-rebuild was a waste of money, but I won't dwell on that, at least Betsy's back on the road.

Thanks all,

Aaron Rochard

1976 230.4 W115

Hello,
I know this may not be of much help now, but the idle cut-off solenoid on the M115/M102 engine works sort of in reverse, it requires 12volts to cut off the fuel flow, there is a relay that applies 12volts for 6-10 seconds after the ignition is turned off to stop the engine. When the engine is running, there is 0volts to the cut-off solenoid. Mercedes engineers are too clever by half as this makes the device *fail safe*: No power to cut-off solenoid, car will not stall at idle.
Have a good weekend.

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Nachi11744

Thanks for the advice, actually, I was looking for a new/rebuit solenoid to put in my car. ( as the car does run on a bit now that the solenoid is unplugged)

Are you saying that the problem lies elsewhere ?

Is it possible it's a needle issue.

Please let me know what you think.

Thanks,

AARON ROCHARD

1976 230. 4 W115.

ive been through alot of the same problems and it turned out to be a little pressure valve on my fuel pump was releasing pressure slowly so if my cart sat for more than 5 min it wouldnt start and sometimes if i shut it off and tried it again it wouldnt start but for some reason it would start on various occasionsby the way my car is a little different 72 280 sel 4.5 but u never know. try checking the fuel delivery system, pump etc.

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1972 280sel 4.5

Aaron,
Does the unplugged solenoid wire have power all the time while the engine is running? Does the engine die if you connect it to the solenoid? If so, the solenoid is probably OK and the problem may be the relay, that nachi11744 talked about.
If you can live with it the way it is now, it might be OK to leave well enough alone.

Happy Motoring, Mark

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DrDKW

Hello,
The unplugged solenoid will let the engine run as it is *off* (0Volts) with the engine running, or the ignition on, for that matter. It activates thru a *delay relay*, like the relay for headlites that stay on for a few minutes on new cars. The relay supplies 12 volts for about 6-14 seconds after the ignition is turned off, blocking the fuel feed thru the solenoid with a pin.

The other suspect with this carb is the *fuel return valve*, a vacuum activated valve that returns fuel to the tank at high vacuum in the carb throttle plate area. The valve could have a leaking diaphram, allowing raw fuel to feed into the carb venturi or the small vacuum hose may be leaking, allowing an air leak plus causing the carb to flood sometimes. It is the triangular cover with three screws under the fuel inlet and return pipes.

Then we have the auto choke, probably the number one reason W115 200, 220 and 230.4s have been scrapped ! It is a simple device that fails and feeds a rich mixture to the engine, destroying it with overfuelling. As my car is in the tropics, I have no need for a choke and I have sealed off the fuel feed and delivery passages to and from the choke. It is, of course, all seized solid anyway.

I did have to replace the main carb body as the throttle shaft was rattling around in it's bore. I found a cannibalized carb where all the component parts had been stripped off and sold, so I bought the (new) body for $80/ and rebuilt the carb around this body and after a careful mixture adjustment have a smooth running engine that idles at 750rpm with a/c and other comsumers running.
Last time I checked in the US, a new carb was $2300/ and a choke unit was $780/ from Mercedes Benz Classic Center !

One last check would be the condition of the float unit. I have come across the *old* floats mysteriously sinking in the *modern* fuels. The new replacement part is a material more compatible with the *new* fuels as the M102 carb engine was using a Stromberg 175CDT until as late as 199X ROTW(rest of the world).
Hope all this rambling is of some help.

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Nachi11744