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  #31  
Old 05-04-2019, 07:26 AM
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Thanks for that. I struggled to understand/execute the "match the RPM drop" with the idle speed adjusters. I mechanically matched the very slight primary butterfly openings with them as a baseline during reassembly but clearly that was the wrong way to go. So since the front has a rather large drop and the rear almost none, I will attempt to balance that out before any more digging in.

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  #32  
Old 05-05-2019, 07:07 PM
Joe
 
Join Date: May 2019
Location: Connecticut
Posts: 92
Hi Ed...
The old MBs are great when they run fine but can drive you nuts getting them to that point. I don't know if it will help you here, but the British use something called a 'unisyn' to balance carbs...it has a plastic ball that lifts to measure the air flow through each carb...they cost only $20 or so and are basically a thin venturi with a draft gauge attached. One thing to be aware of with the early MBs is that the distributor can 'walk' up if not tightened down. Dumb design having a hex nut pointing toward the fan you cant see but have to feel for...I've had this happen to me many times setting the timing on my 280SL...just when I think everything is set, loss of power and sputtering happens when my points move and/or that distributor starts to lift up (and with a flaky condenser). I run mine also using points to trigger and electronic ignition so I have a backup on the road if I want to run full current through the points if the electronic fails...whatever, suggest you get an electronic ignition...it will make your life much easier while chasing everything else. Only like $130...good luck...keep us informed...
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  #33  
Old 05-05-2019, 07:35 PM
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I had about 10 minutes to work on the car today and I switched the idle speed linkages between the front and rear carb without touching anything else. Well, I have something wrong with those because the car fired up and revved to 4k and stayed there. I dialed it down to about 2k but could not get it any lower by hand so I bagged it and am going back tomorrow morning. Not sure how I got them so out of whack but clearly, they are doing very different things.

I have a few hours tomorrow morning to dedicate so am going to start over with those linkages. I saw a baseline setting for them on a BMW forum and will try to find that post again. I don't even know where to start with them. Tight, loose, somewhere in the middle? I was using them set the slight butterfly gap but obviously, that was just wishful thinking. I do have a unisyn tool and caps but with all the raw fuel dumping from the front carb and the tendency to stall often after warm up, I have not had enough clean idle time to work with them for long enough to begin to sync. When I did have it idling better, the rear was pulling no vacuum and the front was pegging the gauge. I do suspect the rear idle circuit was blocked a bit but I think I have that cleared now as I can get air through there and blocking the hole does actually cause an RPM drop. We will see if there is any progress tomorrow.

Thanks!
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  #34  
Old 05-05-2019, 08:08 PM
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I saw 50.8mm on the BMW site.
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  #35  
Old 05-06-2019, 05:34 PM
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Worked on the car a little today. I just made the linkages the same length to start (50mm). Cold, the car starts right up, high and smooth idle then slows after a minute and settles into 900 rpm, still smooth with almost no engine vibration. The chokes open during this time and right before they are all the way open, the idle slows and the car stalls. The car gets harder to start after a few rounds of this. Once warmed the car stalls too often to try to sync the carbs. I pulled the fuel/air screws out and blasted some carb cleaner into the tiny air hole up top and the cleaner jets right out the fuel/air holes.

After putting the linkages back on today, I see a slight dribble of fuel out of both mains. Not a lot but there is some. If I block the air hole for a few seconds, the dribble stops.

I am picking up a gummy set of 72 carbs next week and will get those cleaned up and then can at least have some other carbs to test and learn on and see if they are any better.
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  #36  
Old 05-07-2019, 09:53 AM
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Post Hot Idle Stalling

? Are the throttle shafts loose in their bores ? .
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  #37  
Old 05-07-2019, 11:21 AM
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I believe the throttle shafts can have bushings installed if they are loose.
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  #38  
Old 05-07-2019, 11:37 AM
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Post Throttle Shaft Re Bush

Yes and -some- carbys are made with replaceable bushings .

Choose who you allow to do this *very* carefully.
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1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

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  #39  
Old 05-07-2019, 12:14 PM
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Throttle shafts are tight.

Update! I really thought about the idle linkages while at the car today and with some adjustment from square one, there is no more dribbling from the front or rear carb. The car idled well for 15 minutes while I attempted to sync. I could not quite get them to match on the unisyn but am excited about the new ability to idle. The temp gauge was parked at 175 and the chokes were fully open.

The rear carb is not pulling as much vacuum as the front on the unisyn. While trying to sync, I got them closer by shortening the rear idle linkage and then quarter turns in opposite directions on the fuel/air mixture screws until I peaked the idle out. I got them closer but not to match.

I had it idling (very low) in drive but after more adjustment, it stalled the next time I put it into gear. I did monkey with the vacuum diaphragm to have it pop out and I am wondering if that muddied the waters, who knows maybe that pooching out on the lever was making it worse. I will take it out of the equation tomorrow. The PO did not have the adjust screw installed. Taking a breather and will go back tomorrow.
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  #40  
Old 05-07-2019, 12:24 PM
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Question Dual Carby Adjusting

? Isn't it a progressive 2 venturi carby ? .
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1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better
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  #41  
Old 05-07-2019, 12:59 PM
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Yes, I just think that I may not have them running well enough to introduce that additional throttle input. Just a thought and I want to step back a little and eliminate it until I get everything else better.
Thanks!
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  #42  
Old 05-08-2019, 10:54 AM
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Post

So then .

Disable the secondary venturi and linkage and set the idle mixture on the first venturi then go back and fool with the second one .

Or, maybe get a copy of "The Mercedes Benz Technical Companion" as it has a few articles devoted to proper throttle linkage set up and adjustment .

About $35 when I bought mine .
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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better
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  #43  
Old 05-09-2019, 04:15 PM
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Thanks, the book is on the way.

I picked up a set of carbs from a '72 this morning and they are soaking now. I debated on getting them or not but for the price, they were worth it for the accelerator pumps alone.

They are 32/40's, should I bother even trying them on my 1970 or am I going to have other troubles due to the size difference? I understand that the 72 engine is lower compression but does this matter going the other way in my case?

Either way, I am making them squeaky clean and enjoy the tear down and rebuild process.

Edit. Thinking about it, aren't the Weber's 32/36? Thinking the 32/40 will be fine.

Last edited by Number400; 05-09-2019 at 05:14 PM.
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  #44  
Old 05-09-2019, 05:37 PM
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The compression ratio of an engine is not a factor in the selection of a particular model or size of a carburetor.
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  #45  
Old 05-15-2019, 05:47 PM
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I took a step back and started over on troubleshooting. Vacuum is down and I think I traced the leak to those scary asbestos looking gaskets between the intake and exhaust manifolds. One is crumbling on a corner and it chips away easily. My revs were increasing when spraying carb cleaner in that area.
I took off the carbs and tried to reach those 4 nuts but they impossible. I then loosened the intake/exhaust manifold and exhaust bolts but one of the studs is unscrewing from the engine and coolant is coming out of the hole. Is the stud really holding back coolant under the intake mounting bolts?
Oh well, looks like I need to put my driving plans on hold and rip this thing apart.

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