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  #1  
Old 09-16-2021, 10:13 PM
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Location: Rockford IL
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Getting Ready for the Road.

Just bought the car, going to do an all around maintenance on a 1971 250C.

But I have questions..

spark plug recommendations? Your favorite with part number if possible.

Oil Recommendations: I know.. opening can of worms. I used Castrol GTX racing oil in my 928S because of the high zinc levels. I had 15-40 recommended as a weight from the previous owner in Colorado. I live in Rockford Illinois about an hour and a half NW of Chicago.

The car has some strange looking plug wires, pic below. Bosch Brand. I looked at them in the dark and they are not sparking on the outside, but I am getting a random miss when hot, replace? Problems with the Zenith Carbs also, so it may have little to do with ignition.

Getting coolant out of the water pump weep hole, so that has to go, will replace all belts along the way.

All replies are much appreciated Sirs! Gary

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Getting Ready for the Road.-plug-wires-2-25%25.jpg   Getting Ready for the Road.-plug-wires-25%25.jpg  
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  #2  
Old 09-16-2021, 11:43 PM
Tony H's Avatar
Tony
 
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Location: Bandon, Oregon
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Pertronix is always a good idea. Not sure if you car has the ignition amplifier but it bypasses all that.
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W111 280SE 3.5 Coupe
Manual transmission

Past cars:
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  #3  
Old 09-17-2021, 02:55 AM
250 Coupe's Avatar
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Those look like the original plug wires, at least at the plug end. I’m pretty sure I used a Crane Cams ignition conversion in the 250C but it could have been a Pertronix. Either way, it did run better after the conversion. The 250/8 had points controlling an electronic ignition which worked ok until the points developed a non conductive film. The ex was not happy when the car died on the way to work.

Michael
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  #4  
Old 09-17-2021, 05:12 AM
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Pertronix

Quote:
Originally Posted by Tony H View Post
Pertronix is always a good idea. Not sure if you car has the ignition amplifier but it bypasses all that.
Hello, thank you for your reply.

There is a black box on the drivers' inner fender with a red light on it, is that the amplifier? So the amplifier is good or bad?
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  #5  
Old 09-17-2021, 05:25 AM
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Location: Rockford IL
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Electronic Ignition

So, the vote around here in favor of the Electronic Ignition? Is anyone still
running points ignition?

My Current MB Guru is Pierre Hedary and he seems to think that most
of the problems with points ignition system stem from cheaply
manufactured condensers and that worn distributor bushings cause problems
with EI. But his big complaint is that making the switch takes the grunt
out of the engines' performance.

The last points ignition I used were on British Cars and they seemed
to do ok as long as I did not leave them on and not running for extended
periods of time. Other than that I have no opinion, but yours is very
important to me!

Also, I am putting together an order and I want to buy plugs, please tell me what you use
even if they are not special.

If those plug wires are original, shouldn't I change them? I am
in the habit of doing that about every 5 years on my US Made vehicles..

Thanks.. G

Last edited by glmoore0001; 09-17-2021 at 05:46 AM.
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  #6  
Old 09-17-2021, 10:33 AM
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I’m not sure when Mercedes started using the electronic amplifier with points. My ‘68 250/8 had it. The problem was that since the points were switching low voltage and current, they lost some of the “self cleaning” action that just a bit of sparking provides. They required an occasional cleaning with a business card to keep the ignition in top shape.

I went optoelectronic in the 250C and either the 280C or 450SEL. I may have done it partly due to marketing but did like the results. The 250C started instantly and seemed to run better right after the install where idle had been a bit rough before.

I think the original amplifier was in an aluminum housing, you mention a black box with a red light. That sounds like an aftermarket unit. Do you still have points? It might be a points driven CD ignition or an ignition amplifier. If you have a shutter and optical pickup, it’s probable either a Crane or Pertronix.

Michael
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  #7  
Old 09-17-2021, 05:35 PM
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Quote:
Originally Posted by 250 Coupe View Post
I’m not sure when Mercedes started using the electronic amplifier with points. My ‘68 250/8 had it. The problem was that since the points were switching low voltage and current, they lost some of the “self cleaning” action that just a bit of sparking provides. They required an occasional cleaning with a business card to keep the ignition in top shape.

I went optoelectronic in the 250C and either the 280C or 450SEL. I may have done it partly due to marketing but did like the results. The 250C started instantly and seemed to run better right after the install where idle had been a bit rough before.

I think the original amplifier was in an aluminum housing, you mention a black box with a red light. That sounds like an aftermarket unit. Do you still have points? It might be a points driven CD ignition or an ignition amplifier. If you have a shutter and optical pickup, it’s probable either a Crane or Pertronix.

Michael
No, no points and yes there is an optical pickup in the distributor. i will look a lttle closer and see if I can pull any information from the unit. Thanks.. G
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  #8  
Old 09-23-2021, 11:08 PM
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Regarding plugs, if you search this forum you'll find lots of advice that can be summarized to...

- WDC7 Plugs unless you need WDC6.
- No R in the plugs, unless it says "R0"; you do not want resistor plugs.
- No fancy metals, just basic copper plugs. Not platinum, iridium, fancy forks or anything else.
- There is a spec published for total resistance of the wire and the boots. Check it to know if your wires are any good. A look at the scope pattern at 4,500 and idle is also a good idea.
- The timing would be set at 4,500 rpm, plugging vacuum lines to the distributor and then checked at various RPMs. Also check the dwell at various speeds to ensure that it doesn't change more than like 2 or 3 degrees from idle to that high rpm.

-CTH
PS. Get the ignition to spec before worrying too much about the carbs. When you deal with the carbs, the book says you want more than half a tank of gas in there. Make sure your tank strainer is clean.
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  #9  
Old 09-28-2021, 08:40 AM
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Quote:
Originally Posted by cth350 View Post
- The timing would be set at 4,500 rpm, plugging vacuum lines to the distributor and then checked at various RPMs. Also check the dwell at various speeds to ensure that it doesn't change more than like 2 or 3 degrees from idle to that high rpm.
-CTH
The Electronic Ignition is a Crane Cams FireBall XR700

And the vacuum to the distributor has no vacuum hose going to it, wide open. Should there be one or should that connection be plugged?

If running a Electronic Ignition should I still plug that connector when checking timing?

Thanks.. Gary
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Last edited by glmoore0001; 09-28-2021 at 10:58 AM.
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  #10  
Old 09-28-2021, 11:05 AM
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I used the XR700 on one or both of my conversions. It worked fine for me.

As for plugging the vacuum line, normally there would be a line from a ported vacuum source which may or may not have vacuum on it at idle. You pull it at the distributor to remove any advance it may be inducing and plug the hose to eliminate the vacuum leak created by pulling it off. It may be that a PO did away with vacuum advance altogether.

In the bowl of the distributor, under the points/pick up, there are some weights and springs. This is the mechanical advance. As engine speed increases, the spark needs to happen earlier. Centrifugal force pulls the weights out which causes the part of the distributor shaft with the lobes on it to rotate. That changes the timing of the spark. By running the engine at 4500 rpm, the mechanical with be “all in”. Setting the timing this way may leave you with the timing off at idle but should give you what the engine wants.

Because you have an optical pickup, you won’t have a dwell adjustment. By adjusting how open the points are at the tip of a lobe, you vary the ratio of open and close. It’s important to give the coil time to do its thing, dwell is this time. I don’t remember if the XR700 changed the dwell based on rpm, some aftermarket ignitions do, some don’t.

Michael
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  #11  
Old 09-28-2021, 12:57 PM
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The very comprehensive manual for the XR700/XR3000 can be found here.

Michael
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Current have, 1983 300SD 126.120
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  #12  
Old 09-28-2021, 03:43 PM
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Thank you for the information Michael!

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