M130 engine won't hold idle - Mercedes-Benz Forum

 
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post #1 of 7 (permalink) Old 04-29-2012, 06:27 PM Thread Starter
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M130 engine won't hold idle

Hello all,

I am new to the forum as I just recently purchased a 1971 Mercedes-Benz 250C (M130 with twin Zenith carbs). I have visited this forum quite a bit when I was making my purchase - you guys are great.

We'll I've picked up the car after a fresh paint job and a general "tune up" (new plugs, wires, cap, rotor, transmission fluid change, oil change) and am seeing a problem that was not there when I test drove the car a number of times before the light restoration - the car starts fine, but it just simply won't hold the idle and keeps on shutting off. With revs up it runs just fine, but at idle it shuts down.

I know that this is definitely a problem with so many causes but I thought that I would try the experts to see whether this is a common issue and where I should start looking.

Thanks all in advance.
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post #2 of 7 (permalink) Old 04-30-2012, 06:03 AM
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How low are the revs at idle? Perhaps a simple idle adjustment?
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post #3 of 7 (permalink) Old 04-30-2012, 11:16 AM
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If timing and vacuum advance are correct, try turning the each idle fuel screws 1/2 turn open.

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post #4 of 7 (permalink) Old 04-30-2012, 03:01 PM
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Quote:
Originally Posted by Majkelangelo View Post
the car starts fine, but it just simply won't hold the idle and keeps on shutting off. With revs up it runs just fine, but at idle it shuts down.
I could be wrong, but I think that the zenith carbs have an electronic shutoff for the idle jet. Basically if the car is off, it closes the idle jet. See if there is a place on the carb(s) where there are wires connected and see if the wires are either hot or not hot based on the ignition being on or off. It is quite possible that those wires are disconnected or not functioning which would cause the problem you are describing.

Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...
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post #5 of 7 (permalink) Old 05-03-2012, 07:10 AM Thread Starter
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Thanks to all for your suggestions! This is my first classic Mercedes so I still need to learn a lot - I am used to the simplicity of my BMW 2002!

So last night I put the old spark plug wires back in (Bosch, 7mm) versus the new BREMI wires I installed (by Karlyn-STI) and the car did start and run better - at least it held idle, although it was not smooth. Is the resistance of the new wires perhaps different? I did not that the connectors had 5,000 ohms of resistance.

I need to sort out the ignition before moving on to the carbs. I am tempted to bypass the transistorized switching unit and drop in the Pertronix igniter. I have a unit already (1867A) which is listed for a 1970 250C so I am not sure whether it will fit my distributor (Bosch 0 231 187 003).

Has anyone switched to Pertronix on this model?
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post #6 of 7 (permalink) Old 05-03-2012, 09:54 AM
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I just installed the same Pertronix unit on my '70 280S with the same motor. It is great, go for it! Can't assure you that it will fix the idle problem, but the car will run better.
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post #7 of 7 (permalink) Old 05-04-2012, 12:31 AM
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Originally Posted by Majkelangelo View Post
I need to sort out the ignition before moving on to the carbs. I am tempted to bypass the transistorized switching unit and drop in the Pertronix igniter. I have a unit already (1867A) which is listed for a 1970 250C so I am not sure whether it will fit my distributor (Bosch 0 231 187 003).

Has anyone switched to Pertronix on this model?
The original setup with the transistor trigger was state-of-the-art in its day, reliable, produced a strong spark and good cold weather starting. The special coil (light blue Bosch KW series, often confused with the darker "bosch blue coil" for the VW aftermarket, which is NOT the same coil) was the best Bosch had to offer at the time. Porsche had been using the setup in racing a few years before it was standard on the MB's.

The Pertronix ignitor (make sure to use their coil, too) is fine if you don't want to mess with a poorly maintained factory setup. If your stock ignition is in reasonably good shape, might as well keep it and/or fix it. You won't notice an improvement switching to Pertronix. Yeah, there's points to deal with, but if your distributor isn't worn out they last a long time.
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