HELP! I don't know WHAT is wrong with this car!!

[bachlauter]

Hey!

I did remove that vent valve with the rubber band. It was after reading Dan's post where he mentioned that that thing didn't matter anyways....and other people have said theirs was missing too, so I just kinda figured....

About the mixture screws...yes I did start fooling around with them yesterday too. I turned them all the way in and backed them out 1 1/2 turns ccw and then another 1/2 turn ccw....so they are 2 turns out. I hope I didn't break the end off again....

But here's my new thought....isn't the dashpot for deceleration?? Doesn't it make it so the throttle doesn't SLAM slut when one steps off of the gas?
Well, my problems is when I'm at idle and STEP ON the gas....kaputs everytime! That's probably a mixture problem? It does sound like it's backfiring too, when it's stalls...

Interestingly enough, if I baby the gas pedal and ease it down, the car won't stall. But if I step on the gas (like a normal driver) it DIES!!

I'll keep trying to experiment with the mixture/balance....

~Christy

[DANTRCAV]

Christy:

Yes, one of the functions of the dash pot is to keep the throttle from slamming shut, however; it also serves to kick the idle speed up a tad when rpm's drop. The dash pot operates from manifold vacuum which is higher at lower rpm's. So, in theory, when the rpm drops (a/c on, car in gear, etc) and the vacuum raises; then the dash pot extends to bump the throttle. If your dash pot is operating you should see it move. Example, from under the hood accellerate to 2000+ rpm's or so and the dash pot should retract (manifold vacuum lower). Lower the rpm and the dashpot should extend (manifold vacuum higher).

By the way, I think the cold idle speed is somewhere around 2400 rpms (I would have to check the specs). Also, the rear carb comes off choke slower than the front one as has been pointed out. There are (or should be) two wires to the rear choke cover, one of these is from one of the temp sensors and that is supposed to slow down the opening on the rear carb a tad while the engine get warm (in theory at least). I think I also remember the rear choke being set a tad richer on some cars in the 250 line.

As far as your idle speed dropping down to 600 when in gear I remember mine dropped a lot also but the dashpot picked it back up (when I finally adjusted it).

Interesting to note is that now I get less drop in rpms when I go into gear or turn on the a/c. HOWEVER, and this will probably confuse the issue, but I now run Webber carbs (no dash pot), Crane electronic ignition, and I have disconnected all of the "psuedo emission controll" stuff (one/two way valves, relays, ignition retard, etc). As I stated, I do have my warm idle set to 900 rpms (or maybe 950)!

I don't have my copy of the MB Zeinth manual here at work but if I remember correctly (which us up for discussion if you talk to some people I work with), the erasor on the idle port on top of the carb is used to sync and set the idle adjustment screws and not balance the carb. I will check the manual tonight and if I am wrong I will let you know.

I will check my rpm drop with a tach tonight also to get some precise figures (which may or may not help you one d*** bit).

Dan

[bachlauter]

Guys!!!!!

My mission to locate a dashPOT (or more correctly stated VACUUM THROTTLE CONTROL) is a NIGHTMARE!!!!!!!!

Every used parts joint I called said they'd have to sell me the ENTIRE rear carb...(those dix!!)

And the Mercedes dealership says they don't think the parts are available.....they would only sell it nut by nut by bolt by spring etc...which made me think IS this part REBUILDABLE???? I don't think it is...but I don't know!!!

So......Chuck....old pal old buddy..........you say you have one of these, huh????

Also.... is it possible that my "dashPOT" just isn't adjusted properly??? I have the lowest possible "stick" (bolt?) nearly touching the throttle lever....BUTT that BIG NUT under the spring may not be in the right place.....right??? All I know is that it looks similar to the pictures in my various manuals...

I NEED this part!!!!!!!!!! Somebody SAVE ME!!!!!!!!!!!!

~Christy

[DANTRCAV]

Christy:

Hard to tell about the adjustment unless this little turkey is working. The bolt is used to set the WARM idle speed at approx 1100-1200 RPM, then you lock that adjustment with the locknut on the bolt. THEN, you turn the large spring nut until you get the "index card" or .001" clearance between the bolt and the carb. Not sure exactly how your dashpot is plumbed but on mine there was a short vacuum hose from the dashpot to a vacuum nipple on the base of the carb itself. If your unit is truly shot (doesn't move when engine is raced and allowed to return to idle AND the vacuum connection at the carb is not leaking) then I would say it is shot. If, however, your dashpot vacuum source is from one of the two/three way valves mounted on the fender well (or any other source that is not a direct connection to the rear carb itself), then you may have a problem with vacuum at one of those valves or whatever. I am only familiar with the 250C variant so I cannot attest to all of the other possible ways of hooking up the various "thingies" found under the hood. And, as I stated earlier, I stripped all of that junk from my car a while back.

And, if I had a dashpot I would send it to you tomorrow - but I don't.

Dan

[bachlauter]

Dan!

My vacuum hose hooks on to the base of the carb too.

After reading your reply, I am starting to think that maybe mine is just adjusted out of wack!

When I lowered the bottom bolt, to almost touch the throttle linkage, I didn't turn the big nut at all! I think I've screwed this thing up!!!

I'm going to try to see if I can figure this thing out...

~Christy

[DANTRCAV]

Christy:

What I said about adjusting the dashpot was just what the two adjustments were - not the actual method. Here then, is the method:

1. Warm engine idling at correct speed, remove the vacuum hose from the dashpot and plug the end with something (tape works). You do not want a vacuum leak.

2. Set the bolt to provide 1100-1200 rpms the tighten up the jam (lock) nut to hold this position.

3. Reconnect the vacuum hose to the dashpot

4. Ajust the spring using the large spring washer nut (leave the engine running) until you have the "index card" or .001" clearance between the bolt and the carb. DO NOT LET THE BOLT MOVE OR THE ADJUSTMENT WILL BE WACKO! (and you will have to start back at step 1 again).

Good luck.

Dan

[bachlauter]

Dan!!

Here's the part of the instruction that I don't understand....

Once I disconnect the hose from the dashpot, how can any adjustment to the little screw have ANY affect at all???
I had the car a full operating temperature.
I disconnected the hose..jammed a golf tee in it...(perfect!)
and I started turning the little screw (bolt) on the very end. Mine doesn't HAVE the lock nut. I didn't know which way to turn it!! EITHER WAY didn't make the rpms do anything different.

So...I just guessed (!) and reconnected the vacuum....I THEN started turning the BIG pring nut to bring the little screw DOWN to the throttle linkage....

When I pulled the entire linkage (to simulate pressing the gas)...the DASHPOT MOVED!!! THE DARN THING WORKS AFTER ALL!!!! When I pull back the linkage, the dashpot just barely kicks out to catch the lever....it's now doing what I think it is supposed to be doing!!

On another note....I wanted to recheck the balance with my unisyn.....I discovered that I left it out in the rain and it's not working at the moment.
I dropped the car in gear and the idle sounded really low!!! Disgusted, I shut the hood....the dang tach isn't working now either...and I DIDN'T leave IT out in the rain!!

So...this dashpot probably isn't adjusted right....STILL...but it's now better than it was!!!

Btw...this MB training manual that CTH kindly sent me a copy of, says that turning this screw will make the linkage activate the fuel vent valve....just as Dan says turning this screw will make the rpms change....what the hell am I missing here?? Turning that screw all on it's own, didn't do JACK for me!!!



~Christy

[DANTRCAV]

Christy:

It's a two part adjustment. First, you did good using the golf tee. What you are doing by adjusting the bolt (turn it counterclockwise) so it extends and makes contact with the throttle lever then keep turning until you get the 1100-1200 rpm. If you are missing the locknut it is, I believe, 5mm which are available at any REAL hardware store (like ACE, True Value, etc). If you need to get one, get more than one and save them somewhere (trust me on that one). Once you have set that, then when you reconnect the vacuum hose this will cause the dashpot bolt to move back to some position. Now, you adjust the clearance to the "index card" or .001" by turning the spring nut (again, don't let the bolt turn). What you are doing here is setting the spring tension in order that the clearance is maintained and that the vacuum has something to work against. The spring tension sets the clearance but the relative position of the bolt does not change. Now, when the vacuum drops or when you should see the bolt push against the carb lever. Racing the engine will cause the bolt to retract (remember the "spring tension") and when you let the throttle return the vacuum pulls the bolt back to the throttle until the system stabilizes (vacuum vs spring tension).

However, if you really need to get a lock nut (or nuts) before this adjustment will hold as the bolt will turn (hunt) inside the dashpot assembly. (been there done that).

I guess you have proven the dashpot is not shot otherwise it would not work. Chuck or CTH may be a better answer on this than I but if it works at all then it is holding vacuum and I don't believe it can hold just "a little vacuum" - I would think it was either all OK or all Shot.

Get a lock nut (nuts). Dry out the unisyn. Get the tach working.

Luck...

Dan

[bachlauter]

Dan!

You mean make the bolt actually PUSH the throttle linkage back to raise the rpms....That TOTALLY makes sense!!!

I can't wait to try it!!!

Thanks sooooo much for the detailed explanation!!!

~Christy

[cth350]

Christy,

My email seems to have been out all day at work, since I just got home to read this whole thread (I didn't happen to wander by the site earlier).

All sounds good. Like Dan said, the two part adjustment is designed to (1) set up the dash pot for how it should be have when the vacuum drops and then (2) make sure that its out of the way when the vacuum is high.

As long as your foot is on the gas at something above idle, the throttle is away from the bolt, so it has no effect whatsoever. It's only with your foot off the gas, or when the pressure is so light (and the engine is going so slow), that it actually interfers (hopefully for the better).

That's exactly what's going on when you're making that turn at the stop sign and you stall.

For now, not having the lock nut isn't the worse thing in the world. Since NONE of the early cars had one. You can adjust it, get it going, shout estatically, and then do it all over again, just like an old pro, when you dig up the nut.

-CTH

[ctaylor738]

Christy -

Back in town. I take it you still need a functioning dashpot? Please let me know, and I'll test my spare tonight.

Chuck

[stevebfl]

Sorry to jump in on this so late. I could have told you to forget about those dashpots till you had fixed your problems.

Seems that I read that the carbs were rebuilt. What does this mean? Were all the diaphrams and accelerator pumps replaced? The secondary throttles are opened by venturi vacuum. The car will never see the secondaries if these large diaphrams are broken (and will be real slow).

The prime compensating element to transition from idle air velocity to open throttle air velocity are the accelerator pumps. Without them the power falls on it face during throttle movement. Everything I have read about your condition sounds like a lean condition here. Do you get equal streams from both carbs when hand accelerated WITHOUT the engine running.

Where do you have your timing? Take it at least ten degrees above factory setting and tell me what happens.

[cth350]

Blast! Thanks Steve, I've been asleep on that one. The one thing Christy DIDN'T replace was the secondary diaphram (she was being conservative, only breaking one part of the carb at a time).

Shew reported that the pumps work alright, possibly not copiously. It will be fun to see how she measures that.

Why the reported behavior of it being happy in lower gears (and thus higher RPMs when driving)?

-CTH

[stevebfl]

The problem appears to be in the transition area of the carburator. This is where there is not enough velocity of air to pull fuel properly from the main venturi system. The whole transition event is accomplished by a series of idle hole immediately above the closed throttle plates and the accelerator pumps. As the throttle opens if idle were all that were there the lights would go out like a candle in the wind. Much assistance is necessary. Every condition that leans the overall mixture will also increase the need for transition enrichment. If you can keep the rpms high and the air velocity equally high then transition isn't as becessary as the mains are already flowing.

BTW, the main jets emulsion tubes and air correction jets should be verified for position and size. I have a MB Zenith book at work that gives the jet numbers and positions. If it says that you should have a 115 jet this means .115 (inch or mm - something) a jet gauge should be used to verify the hole size. Many have been reversed or drilled or restricted over the years.

Once I was sure that the float level was good, that the float bowl was vented, that the jets were right, I would probably open up the main jet by .005.

AND I would increase the timing!!!!!!

[bachlauter]

Thanks STEVE!!!!!!! (chant) Steve! Steve! Steve! Steve!

I feel totally capable to do the secondaries!! BUT....OMG!!!!!!!!!!!!! Does that mean I have to take the ENTIRE carburetos off of the manifold again????? (I forget) OR can I just pull that little "arm" off of the lever and unbolt the things and go from there??
I bet I DO need these diaphrams since BEFORE the secondaries were "cemented" shut and ... just the fact that they WERE "cemented" shut means that they OBVIOUSLY weren't working for a long time...

Steve...your response is so technical and knowledgable! I think I'll need to re-read your post (like 50 times! lol) to come up with my next question!

~Christy