Stromberg 175CD, were do I find the mixture screws? / How do i adjust the mixture? - PeachParts Mercedes-Benz Forum

Spray · #1 09-16-2007, 02:25 AM

Where can i locate the mixture screws on this carburettor?

I also wonder how i can check that the magnetic valve is working. Thanks!

ggenovez · #2 09-16-2007, 01:06 PM

looks like the mixture is done automagicaly

http://www.iai.heig-vd.ch/~fwi/cars/docs/SU_carbs_tuning.pdf

I could not find anything on magnetic valve

Spray · #3 09-16-2007, 04:13 PM

hmmm my carb does not look like the ones in the manual... strange!

Spray · #4 09-17-2007, 03:29 AM

Quote:

Originally Posted by ggenovez

looks like the mixture is done automagicaly
http://www.iai.heig-vd.ch/~fwi/cars/docs/SU_carbs_tuning.pdf
I could not find anything on magnetic valve

I have figured out that the mixture is controlled by turning the thing thats located on the lowest part on the carb. Look at this picture, its the one with the cable going into:

(my carb does not look EXACTLY like this but close)

If i measssure the voltage in the cable, i have 12V when the ignition is turned OFF, and 0V when the engine is turned ON. I have connected the + to the cable when the engine is running, but nothing appears to happen when voltage is put on.

Can someone explain how i check if this thing's working? Whats the purpose

meltedpanda · #5 09-17-2007, 08:50 AM

on the bottom of the carb is the cut off selenoid. This acts to shut down gas flow when the engine is turned off to prevent run on that is common to the venturi type carbs.
you can put 12 volt directly to the wire in (+) and you should hear it click. YOu can also unscrew it but you run the risk of damaging the small O ring
This is also your lean rich mixture , very small increments make a world of diffrence.
I have rebuilt several of these and have a ton of information if you want it just PM me.
Good luck

Spray · #6 09-17-2007, 11:34 AM

Quote:

Originally Posted by meltedpanda

on the bottom of the carb is the cut off selenoid. This acts to shut down gas flow when the engine is turned off to prevent run on that is common to the venturi type carbs.
you can put 12 volt directly to the wire in (+) and you should hear it click. YOu can also unscrew it but you run the risk of damaging the small O ring
This is also your lean rich mixture , very small increments make a world of diffrence.
I have rebuilt several of these and have a ton of information if you want it just PM me.
Good luck

Thats very intresting! Ive been looking for a guy like you for a long time.

If I put 12V on the solenoid the engine should stop running, right? That does not happen.

When it comes to adjusting the mixture, Do you know how far out the solenoid should be as a basic setup? How many turns from the total cut off (as far in as possible)?

Spray · #7 09-17-2007, 11:37 AM

Here is my other thread about this problem

Mercedes 200 Compact -75, Engine wont run on all four. M115 Stromberg

meltedpanda · #8 09-17-2007, 11:45 AM

Quote:

Originally Posted by Spray

Thats very intresting! Ive been looking for a guy like you for a long time.

If I put 12V on the solenoid the engine should stop running, right? That does not happen.

When it comes to adjusting the mixture, Do you know how far out the solenoid should be as a basic setup? How many turns from the total cut off (as far in as possible)?

no the engine will not stop just by activating this, in fact if it is hooked up correctly it will not fire when the egine is running. When you turn the key off it activates a selonoid ( over by the battery) that activates the plunger that stops any more fuel going into the carb, this is activated for only a few seconds and only functions to stop run on.
I tune mine by ear and then run her up hills to see if it needs tweaked. Get it running smooth and then run her up a hill, lack of power? Lean it , a 1/4 turn at a time and then retry, believe me a small turn equal some big changes.
The only real way to tune other than by ear is a exhaust gas analyzer to check for CO levels
Good luck

Spray · #9 09-17-2007, 03:53 PM

Hmm so what happens if this cut off valve is not working, will the engine be able to run correctly anyway? (besides the possiblility of "dieseling" when the key is turned off)

What do you think is the problem with my engine? I just cant get it to idle smoothly. Sometimes it runs on cylinder 1 and 2, and sometimes on cylinder 3 and 4. And some other time it run on all four cylinders, but theres a lot of "bludder" from the exaust just like the car was running at very rich settings.

Today i talked to a specialist on these kind of MB cars. He suggested two possible problems:

1. airleak between carb and the inlet manifold (the rubberplate between carb and manifold). -I checked this instantly and I couldent find any leaks.

2. Crack in the inlet manifold / exhaust manifold that makes the exhaust gases to mix with the air/fuel mixture in the inlet manifold. (Not sure wheter he meant a crack in the cylinderhead between the inlet and the outlet or if he meant a crack between the manifolds...) -I removed the carb and took a flashlight to look inside the inlet manifold. And yes, a minor crack was there, but it could not be the problem since it seem to be a very "tight" crack.

Tomorrow I will try installing another carburettor and I will also replace the ignition coil but I doubt that it will make any diffrence at all.

Anyone feel free to give me good ideas. Im starting to run out of them.

meltedpanda · #10 09-17-2007, 04:18 PM

well cracks of any kind expand and contract, I had one on my exhaust manifold that was worse when cold. Does your car run better when hot, could be a crack issue ( sucking air)

The shut off valve does nothing more than prevent run on, BUT it is the lean/ rich mixture adjustment
I once had an intemitant short in the wire coming off the condensor that caused a miss and at one point would not allow it to start, Check to make sure your electrical connections are not going to ground, vibrations have a way of loosening things up. It was actually grounding on the body of the distributor
Lack of cylinder fire can only be because of lack of fuel or lack of spark

Does your car have an ignition box? that could also be the issue. Sit in front of and under the battery tray in most 114/115s

Spray · #11 09-17-2007, 04:43 PM

Thanks again,

Im i able to setup a correct mixture with the solenoid out of function? Im worried that the solenoid makes the carb diffucult to setup correctly..

Ignition box? Have to check that, whats the purpose of the box? The sparks a quite yellow is that someting to worry about?

-----
I assume that if the sparks are weak, the air/fuelmixture might put the spark out. When the engine runs at a higher RPM, the alternator gives the ingition coil a higher voltage and therefore the sparks are stronger at a higher RPM wich means that the engine runs nicely when driving. Possible or impossible?

Spray · #12 09-17-2007, 04:46 PM

Hmm but then again, if the ignition coil leaves insufficient voltage to the distributor, the sparks would be bad on all the four cylinders, not only on no. 3 and 4....

ggenovez · #13 09-17-2007, 07:17 PM

Spray,

The way I ckeck for leaks is with carb cleaner. It's very flamable so if it gets sucked into the engine you will hear the RPMs jump up by 50-100 RPM.

Spray the bottom of the carburetor and the intake manifolds, and the manifold to head gasket and see if there are any RPM changes.

Make sure you have a fire extinguisher just in case you knock a fuel line loose or something

meltedpanda · #14 09-17-2007, 09:56 PM

a non functioning shut off selenoid will not affect running.

weak spark cannot be "put out" by fuel air mixture

your coil could be bad, could have a short, could have bad spark plug wires, distibutor cracked, distributor cam worn, bad condenser, improper condenser, point set, could be sucking air, try the spray trick mentioned in previous post

lots of could be's

rule them out one at a time

Oh the ignition box is the "first generation" of eletronic ignition, helps to regulate spark
DO a search under ECM or Electronic control module.