INAT idle stop screw setting
 

Hi all,

I have a 72 250 M130 US with the original Zenith INAT 32/40 carburetors. The Haynes manual states that the gap of the idle stop screws is supposed to be 2.3mm and stop at the float house venting valve.

On Jaime Coplands site, it states that venting valves where for pre 72 vehicles, but does not state how to preset the carbs.

on a just rebuilt carb, what is the preload needed for the idle stop and adle adjuster nut? on a BMW site http://www.cscoupe.org/tech/zeniths/bmw1/bmw1.html#004 it states to set the initial idle adjuster to 50.8 mm. I guess it should be just touching at that setting? is that correct or is there something different for the benzes.

Also, is the linkage supposed to be installed with the anti-stall device backed off? I would immagince so, otherwise the rear carb would not be synced. Is that correct?

Thank you all for you help.

George

Hi George,
I am working on the same issue for my 72 250 with 32/40's and I had some initial luck setting the distance at 56mm as measured from the bottom of the linkage to the top of the idle stop. (not the length from disconnect to disconnect) about 3 revolutions from once the threads engage. This allowed me to get her running, but now I am wondering how I am going to get the two balanced without a tool. If you have any tips, or know of where I can get a synchronizing tool that would be great.

I am also looking for a source for the accelerator pump and I haven't had any luck.

You can get a good adjustment with a 2' piece of heater hose to your ear, listening at the base of each carb and adjusting to equalize the sound level. IME, the tools don't give much better results, because it is very hard to equalize the seals between the tool and the carb tops.

I always thought that you adjusted the stop so that the vent just opened when the arm rests against it.

I think I have one accel pump left. Pls send me an email to remind me to look for it when I get home on Friday.

Hey Blue,

Yeah I just used a vacuum hose, like Chuck said and you can definately hear the differenace.

Be sure the engine is not backfiring!

I'll try the 56 mm.

Chuck, 72 onwards (last year for zeniths?) they removed the vent and replaced it with a bolt & nut.

From http://www.jaimekop.com/CarbManual/Page04-05/index.html
"The venting valves were eliminated on 1972 models in order to conform to federal requirements. Only internal venting is provided on these models. "

Thanks for everybody's help.

Blue,

you mentioned 56 mm that's over 2 inches. I don't think I follow where you're measuring from. here is where I'm measuring and I'm getting 11mm and that is just engaging the leaver

I must have been wrong when I quoted the 56mm. I was refering to the idle adjuster nut, not the stop nut.

Thanks for the tip on the heater hose, I will try it when I get a chance.

I am still having hesitation off the line even though I have better Accel. Pump performance. With out measuring the amount I would say that the two pumps are close to the same output. Is there any other reason that I could have the hesitation? I dont feel that it is a timing or ignition issue as I am 12 btdc. Any thoughts on the issue would be helpful.

Thanks fellow Benz Lovers

When you say hesitation do you mean it's bogging? RPM's drop and kind of limps along but runs great when you start to accelerate?

Trouble uphills especialy off start?

Does the car want to stall when you cover either carb with a shop rag?

12 BTDC is that with the advance on? what RPM? that sounds a little on the high side.

Also, if you have a caliper and can measure that distance I would appriciate it.

Where did you get 56 mm for the idle adjuster nut?

Just thought I would throw this in. I assume everyone working around these carbs is aware that light to massive air leaks do happen around the base of the carbs. The gaskets that seem more like heat isolators seem to age poorly and there are two of them for each carb. The first thing I always did was take a can of wd 40 and slowly spray around the bases of those carbs to detect if there. I know or suspect you all know this but just in case someone does not. I also liked the hose ideal that was mentioned. I took a motorcycle carb vaccum setup for syncronization years ago and turned a wooden recessed disk on a lathe to cover the large zenith air intake with a smaller hole drilled in it to mount the gauge to. The original air cleaner O ring seals it. So if you see a carb syncronizer for motorcycles you can make adapters for it. This is the most common one to find now at least used and cheap. Another thing was cleaning these carbs out from dried gas residue. Just making them run on laquer thinner and letting them sit and soak for about 20 minutes seems to dissolve any in the idle passages etc. Engines seem to run pretty well on the thinner as well. Suprised me. Sure beat taking them apart and soaking and kitting them in most cases for a residue problem. I have seen completely obstructed idle passages for example clear in 20 minutes. In fact my first test to see what the carbs internal passages are like is to pull the idle screw and watch for how much flow of gas comes out. Many times the improvement on a carb you thought was okay even has been substantial. Needless to say if there are other internal faults you will still have to deal with them. If I remember right but allow it's been quite awhile since I worked around these engines and I m only an amateur mechanic at best. Where is this 12 degrees coming from? Things do change but I seem to remember timing was set at about 3000 rpm and somehere around 30 + degrees was required. I know it will be far less than that at idle but it was not recommended to time them there. I could be wrong and often are but you want to eliminate that area for sure. Someone with greater knowledge than myself should chirp in if I am right or wrong about the timing issue. Oh yes I just remembered There is a vaccum fitting usually around the sixth cylinder. I caught quite a few of them leaking air in resulting in the cylinder not firing or weak. Always pays to check with wd 40. I only hope my memory is accurate . It might not be in certain areas. It's been a long time.

Barry- thanks for the insight, your memery is accurate on the vac. line coming from #6 intake. I assume that it is for the vapor recovery in the gas tank, the line is intact on my car and I feel that all possible sources of vac leak are tight. I also heve new gaskets on the plates and shims, the Walker rebuild kits I got were short a few so I had to play craft time.

As for the hesitation, I can say it is a bogging. If I "pop" the throttle off of the line, rpm drop and then it picks up. If I ease into the throttle there is no problem. My rebuilds went well, I have excelent performance other then then off the line. The old girl gets moving when the secondarys kick in. I do feel a little guilty runnung her out that far given her age though.

As for the 12 btdc I am at 1200 rpm (my current idle ) and vac advance hooked up. When I spin it up to 3000 rpm I am in the 30btdc. I was running this car at 5200 ft and it seemed to run better there. I am now at 1100 ft and I think that lower timing could be justified but I dont want to mess with it until I get the carbs running the way they should.

I will be able to provide more information regarding the bogging, after I get to it this weekend. I would like to work on tuning the carbs before then but I am getting behind on my school work this week from the carb rebuilds. Not to mention that the wife is going to kill me if I dont spend some time with her.

I am looking ofrward to any more insight that the community has regarding the Bogging or hesitation.:kid:

Blue:

If you search this site for "zenith+carburetors", and "230/8+zenith" you will find several threads on living with and caring for your trusty Zenith carburetors. They are much better than their reputation suggests.

Your idle speed seems quite high. I believe it should be somewhere around 800 to 900 rpm. Once you get the idle above 900 rpm you will notice the centrifugal advance kick in and raise the engine speed, to about 1200 to 1300 rpm. I suspect once you have sorted through the somewhat tedious carb adjustment process and get the zeniths all balanced as they should be, you will be able to set idle into a more normal zone.

If your advance is 30 degrees at 3000 rpm, then your distributor is spot on. You should have 35 to 37 degrees at 4500 rpm and 25 to 32 degrees at 3000. Some cars take 0 degrees initial timing at idle and give 35 to 37 at 4500, others need 2 to 4 degrees to get there.

The factory CD ROM is chock full of good information for tuning these engines (engine repair PDF 00-0 is the section). It is a bit sketchy on many things, but the tuning information is pretty good. It also contains the factory data for Zeniths. Get is here for $20:

http://www.classictechlit.mbusa.com/MB/

Another good value is the chassis manual which is also available for only $50, same site.

Excellent balancing tools are available here; locate them with a search on "zenith."

http://www.baumtools.com/


I suspect you will not be satisfied with adjustments made by listening through a heater hose. Perhaps your ear is better calibrated than mine, but after 30+ years of tending to Zeniths I have never had a good result using a hose to my ear. You really need a Unisyn and a proper carb-top adaptor, which in a pinch you might rig up with a Cool Whip tub, about the same diameter as I recall, but a bit flimsy to make a tight seal. I got my top adaptor from a Solex agent in Vienna, but the Baum item looks identical.

Best of luck with your efforts,

230/8

Vent valve adjustment
 

With the engine fully warmed up and choke wide open and vacuum throttle retracted the travel on the valve plunger should be 2.5-2.8 mm.
Accelerator pumps try www.royze.com
You should use only one syncronyzer and two adaptors which you can make from sheet metal,the same engine conditions are used.
Mike

Looks like my thread was succesfully highjacked ;)

Any more info on the non vented zenith carbs would be greatly appriciated.

Thx

George:

Sorry for losing the plot...

I suspect the Haynes manual you are using is making reference to a specification for a european version, or an older version of the US models which have adjustable vents. My Haynes manuals seem to mix a bit of stuff here and there between euro and US models. The USA versions for 72 do not have adjustable external vents...the venting is internal to the airhorn of the carburetor. There is a linkage stop screw on each carb which should seldom if ever need adjusting. It is a rest for the throttle linkage and should be evenly set on front and rear so the bell-crank linkages are operating from rest with more or less the same geometry. I do not recall a particular specification for the stop, only for adjusting vents in relation to the stops.

As to the idle...once you start fiddling with the carb adjustment/balance/dashpot/linkage you will need to be systematic, and I refer you to the site search mentioned to Blue which should assist your understanding of the procedure. It is amazingly simple once you take time to study the process and results of an adjustment. Proper tools will be essential.

For balancing and idle speed adjustment the dashpot must be backed off so it does not touch the linkage. The F/R connector linkage is recommended to be removed, but I have never found this to be necessary...if you do remove it, you will need to re-check your F/R balance after re-connecting it. Once you have attained the magical balance of the carbs and the engine is running at the proper curb idle speed you can begin to adjust the dashpot for its curb idle setting and in-gear (for automatic transmissions) speed setting. Use the Zenith book as your guide because everyone else steals the data and re-prints it. Dashpot setting is also a trial and error process, but also amazingly easy.

The manual on the JaimeKop site looks like the MB factory manual, which is available from MB Classic at this site:

http://www.classictechlit.mbusa.com/MB/

I heartily recommend getting all the available tech data if your intent is to keep and enjoy this car. The factory CD Rom is pretty good, the chassis manual is excellent, and the Zenith manual will be very handy, too. Another potential source of information is:

http://www.books4cars.com/

For the most part, having the chassis manual, Zenith manual, and CD ROM will be necessary to fill in gaps in Haynes and Chilton but most especially concerning anything to do with the body. The factory engine, transmission, and HVAC manuals may be hard to get. Haynes and Chilton have some good information, but most is simply a condensation of factory stuff with poor reproductions of factory photos.

Use the search for this site for excellent anecdotal information from the personal experiences of real DIYers and generous professional service techs.

Good luck,

230/8

Not a problem with the highjacking. In fact I kinda started it.

I already have the chassis manual from MB, and the CD Rom. If the MB manual is identical to what is available on the website, I'll pass for the moment and continue restoration.

Is there any chance you have a scanner and can email or upload a copy of the 72' US carb section?

I guess my biggest problem is to figure out how to drop the RPM from 1400 to idle. Loos like no matter how much I fiddle it's running way too fast.

That's whay I'm looking at the idle stop and the idle adjuster linkage and trying to figure out how to set it back to factory.

Thanks again.

George

Sorry for the hijacking
 

I thought that I could give a little insight to your problem as I am having the same problem with the curb idle and adjusting my carbs post rebuild also.

again, sorry for the hijacking:ukliam3:

Let me know if you find the illusive "sweet spot".

I did order the baum synchronizer today, so if you want to use it when I am done I would be happy to mail it to you.