Carburetor (07)

For control arm, see Fuel pump and air filter.

Mercedes-Benz Motor M 180 II for Ponton type 219, Sechszylinder, 1956 - 1959., © Daimler AG

As with some other parts this had to be done more than once. Here we go...

The first round

First the carburetor, a Solex 32 PAATI, was totally dismantled, everything was marked and I made a drawing on how everything was assembled (note however, that you always forget to draw the most important thing and that it may have been assembled incorrectly). Thereafter the parts were washed with a carburetor cleaner from CRC. All plane surfaces (normally the ones where the gaskets etc sat) where leveled with hard, fine sandpaper (silicon carbide paper?).

After that, everything was put back together again, with all holes stuffed up. And after that came the fun part, glass beading with 150-250 micron glass beads (which may a little to big?!) using 6 bar. This gave the carburetor its original finish back. Some small areas are however a bit granulous. The funny thing is that the items first looked rather blotchy, but after a couple of days the surface got an even, light grey color. All screws etc were re-finished in yellow and necessary gaskets, diaphragms and other items ordered.

Sorry for the bad photo quality, there are more photos but I think they'll only be usable for me...

After the beading I had to take a photo of all the parts involved (partners get used to this after some time). The last picture shows you the assembled jewel.

I had some issues with the screws for the accelerator pump. They are supposed to be M4*0,75 (why didn't they use M4*0,5 - fine?) which I also ordered from Karasch. Unfortunately, when the carburetor was overhauled ~15 years ago the shop "repaired" (awfully bad done though) these threads with M5*0,8 (coarse). I didn't realize this until now. This was followed by long discussions with the guys on the Ponton list as well as with the Swedish MB list with a lot of valuable ideas coming out. After some time I settled for the easy solution, installing Helicoil M5*0,8 (thanks for the help Colly Company) and bought screws looking like the original ones. They were yellow plated as the rests of the screws and nuts. But I suppose that the other suggestions will come in to use on other parts.

Conclusion, be very careful with what threads you are working with. If you look in the spare parts book you can identify all screws and nuts that have these funny dimensions, M4*0,75 and M5*0,75. I don't think that you can find inserts for them but you can find taps and dices. With them you are able to make your own inserts!

When the carburetor was overhauled, they installed new bushings for the throttle shaft, unfortunately not with rubber sealings. Instead they had milled a ~3mm large "hole" on each side of the float housing and sealed the shaft with plastic sealings in these holes. That didn't feel like a perfect solution. I didn't want to put in new bushings with rubber sealings so I tested a couple of rubber sealings to see if I could find anyone with a size that fitted my present situation. I did, so I went for the - in my opinion at least - second best solution. I smeared them with rubber grease and covered the whole thing with the plastic sealings I already had to protect it from dust. The shaft moves like it should and now I suppose it will by tight and let no air through for a lot of years.

The screws that holds the Bowden cable for the choke is a special screw with a fine thread, M5 x 0,75. In my case the threads in the housing are severely worn out at the opening. Reparing with Helicoil inserts is not possible since the pot metal is to thin and in itself too fragile. After a lot of discussions with Will Samples and the technical specialists at Colly Components (and they have been very helpful, sharing their deep knowledge in other areas during this restoration, thanks!!), we came to the conclusion that there's actually nothing to do. The only long term solution is to buy a new throttle part, but at this point I'm not willing to do that. The other solution is to make use of the good threads at the end of the hole, and applying Loctite Medium at the opening. We'll see if it holds.

And again...

Before reinstalling the carburetor on the engine I wanted to double check that it worked after my previous old restoration and also make the basic adjustments according to the workshop manual. The test of the diaphragm/accelerator pump failed; Firstly too little gasoline coming out of the injection tubes, secondly a gasoline leakage under the accelerator pump housing. Only very small one but enough to disturb the pump's function.

The Solex 32 PAATI back on the M 180 II engine

Leakage

We start with the simple problem, the leaking accelerator pump housing. 

Taking the accelerator pump of I also realized that I had been too cowardly when leveling the surface. I didn't dare to take the guiding pin out but tried to get an even and leveled surface around it. But just around the pin, there is a small "hill", enough for making it impossible for the pump housing to attach firmly to the carburetor housing and the rubber gasket to seal. You can see this in the first picture. That was of course not good and taking the pin carefully out with pliers was very easy. Sanded again and got a perfect result (#2) The housing was now "a bit" more easy to level. Also did this on the starter valve which you can see in picture three. In the third picture you can see that the guiding pin has a hole. That was filled with dirt. I cleaned it with a bit of metal thread which is probably not advisable. Should probably have done it more carefully. We'll see... In the fourth picture, to the left, you can see the new diaphragm and the new spring I inserted. To the right is the old spring as well as the new diaphragm I installed when I restored the carb as per above. thought it was better to have something really fresh in there.

Accelerator pump

According to the Workshop manual you are to use a set of extra injection tubes and turn them outside the venture tube and the carburetor body and into a glass measuring cylinder. And you're absolutely not to use the existing injection tubes while doing this. Since I know that I have fiddled with those during the restoration I took them apart anyway, cleaned everything including the surface between the injection tube “housing” and the carburetor and checked the gasket as well as the balls under the tubes (pictures 1 and 2 below). Will Samples told me to seal the injection tubes with epoxy or likewise if they leak after this. They did not however. Getting new ones as separate spare part seemed impossible.

My "test bed" for the measurement you can see in the third picture. You set the amount of fuel by adjusting the nut on the rod. Outside of the nut there should only be a few threads visible. When I took the carburetor apart the nut sat 1,5 mm from the end of the rod (see fourth picture where the distance is 9 mm). The first problem I encountered was that the lever seemed to get stuck from time to time. That was solved by assembling the pump loosely, give "full gas" a couple of times and then tighten everything. That way the diaphragm settles itself in the correct position. After that I tested the pump according to the workshop manual with my "test bed". The pump is supposed to deliver 1,3-1,5 ml per stroke. I did not achieve that. The list below shows distance in millimeters between end of rod and the first nut. (Comment: the values below look odd, will double check them and correct the article as soon as time permits!)

• 2mm => 6,5ml
• 3mm => 7,5ml
• 4mm => 8,5ml
• 5mm => 9ml
• 6mm => ~9ml
• 8mm => 8,5ml

Definitely not good. After a lot of contacts with Will and other knowledgeable club people (above all a huge thanks to VHD Mercedesclubs.de) I started to think that my didn't get pressed out long enough. So I went out looking for a new spring - and a brand new diaphragm (I also bought the same stuff new for the starter valve as per above). Found it and installed it. In the fifth picture you see the new diaphragm I installed during the first restoration, the old one and finally the newest one. The old and the new spring is above. The length didn't really differ between them but you could definitely feel more resistance with you compressed the new. I the sixth pic you can see how I moved the shaft to the new diaphragm. And finally, in the seventh picture, you can see the lever now being pressed out. Before the new spring the lever was pointing out from the carburetor. Another way to look at it is in the last two pictures where you can see that the new spring moved the "pressure point" (where the lever lays on the diaphragm) on the rod, 4 mm!

The first test with all these parts replaced did give me more fuel but still not enough. I gave it up a couple of days. The next time I tried it, I regularly got a nice stream over and over again (and also on the correct spot by adjusting the injection tubes slightly). It obviously needed to sit for a couple of days to really settle in. With the locking nut on the connection rod being screwed in as per below I get the following amount measured over 20 strokes:

• 6mm => 1.05ml
• 7mm => 1.22ml
• 8mm => 1.35ml
• 9mm => 1.55ml

Still a bit too little, but it may also be due to that gasoline vaporize quickly, that I loose some while it's pouring and dripping into the measuring glass. We'll see how the engine goes. The amount is supposed to be between 1.3-1.5 ml so I chose 8 mm.

Parts list for the Solex 32 PAATI carburetor

Another thing that disturbed me for "some time" was that I during my test measurements noted that gasoline was leaking around the mixing tubes if I leaned the carburetor more than approximately 20 degrees, i.e. as if the car was standing uphill (front higher than rear so to speak). See first picture below. I put a lot of thought and mailing into this. I couldn't see exactly where it came from, from the four holes in the mixing tubes or if there was a leak at its base was difficult to say. That would mean that the car would leak gasoline into the engine when you park it uphill. Cannot be right… But then Will asked me to read https://en.wikipedia.org/wiki/Grade_(slope) to see where I could encounter such a situation. Not many. And if the car is sitting on an incline and not running, the fuel will run out until there is not enough to run out anymore. This will be a very small amount. If the car is operating the fuel will be sucked into the engine. Either way, this is not a problem. So now you know too :)!!

Among other things I have replaced are the float needle valve. I didn't thought that would be necessary but when I got the new one and compared their function, what a difference. It is not strange since it's being used all the time while you are driving... Also new idling nozzles and the return valve in the accelerator pump. This you can see in picture 2 and 3.

Putting the Solex 32 PAATI back on the M 180 II

I used sealant on the insulating flange as well as a gasket (I don't think it should go there but my father had it and I didn't want to smear the protecting plate under the carb). A small amount of vaseline went on the paper gasket under the carburetor as you can see in the second picture. The other two pictures show the carburetor in place on the engine as well as with the restored air cleaner on top. 

Next step

Before installing the engine, with its auxiliary systems mounted, I wanted to check that everything worked as it should, do necessary adjustments, re-tighten all screws and see to that I had no leaks, see Running the engine on test bed.