The Running of the Benz – Part 5

Now that you’ve seen Winston complete the Power Tour Long Haul and I’ve shown you a bit of what I do (Don’t worry, blade building is still coming!) I’m going to go back in time and complete my series on getting Winston ready for the Power Tour. I like to do things backwards ’round these parts. This post covers rebuilding the carburetors and then the exhaust work that my brother and a friend helped me with. There are a lot of pictures, you’ve been warned!

The Carbs

In my last post in this series, we left the carbs sitting on the workbench, still attached to the intake/exhaust manifold. Naturally, my first step was to get one of the carburetors off there. Once that was done, I got to work on taking the little bits and pieces off the side and making sure to remember where everything went, as well as where I put the pieces. I actually took pictures of every screw/bolt/nut/clip that came off and another picture of where I set it so that I could go back and look if I forgot. Some of those small linkage bits are hard to move out of place, and equally as fun to move back in later in the rebuild process. It also became clear fairly early on that these had been apart before. Like the little black screw holding the choke linkage in. That’s not supposed to be a screw…


Once the surrounding bit were off and taken care of, I began to take the different layers of the carburetor apart. There are 9 bolts holding the top layer on, 8 around the outside and 1 in the middle. I initially missed the middle one and, luckily, didn’t try to just pry it apart before I figured it out.


The second layer has just 2 bolts holding it together, both near the middle. Once those are out, you got to see where the magic happens. It’s gloriously complex and has a way of making you respect the people that put this together and those that completely understand what all the little passageways do and how they work. Me? I’m just taking it apart and hoping I don’t break it.


Next, I started cleaning all the parts. We have a parts washer, but it’s just filled with old diesel fuel and whatever brake cleaner runs off the parts you work on. It works, but it takes a bit of scrubbing and your hands will cramp. I also didn’t get to soak these parts as long as I’d like, or have all the right tools to clean every little bit, but it was much better than leaving them all grimy. After some scrubbing, I did a final wash with brake clean as it wouldn’t gunk anything up like the diesel fuel would. If I were smart I would have just taken these somewhere that had an ultrasonic parts cleaner or something of the like. Would have saved my hands from smelling horrible, cramping, and cleaned better than I could. Should, woulda, coulda.


Now we actually had to dig into the meat of the rebuild. Find which parts in the kit would fit my specific carburetor, test fit, change the tiny gaskets and seal them with hi-tack. There weren’t many small bits to actually change out as my kit was fairly cheap, so we just changed out what we could and then found the correct gaskets to put the three layers back together.


It actually looks pretty good once it’s cleaned up a bit! The base plate still needed some cleaning and deconstructing though.


Those parts didn’t get cleaned up quite as well, but they still look better than they did. Now the reconstruction begins! I used anti-seize on any parts that were metal on metal, such as the linkage ball joints. The last thing I want is my throttle getting stuck open, or closed.


Once I had all the little bits stuck back on I lined everything back up on the manifold and put the carburetor back on. With a side by side you can see how much better the rebuilt carb looks.


On to carb 2! Same as last time, tearing everything off, give a good washing, check all the parts to see if they need to be replaced, and set them aside while hoping you remember where everything goes. These pictures go a little more in depth to show how everything fits together.


This is what happens when gas sits too long, it turns to kerosene!


A nice shot of the second and third layer. The third layer on the right is basically just the float bowl. This bowl fills with gas via a “needle”. There is also a “float” in this chamber, a hollow plastic piece who’s purpose is to float up as the gas level rises in the chamber. Upon floating up enough, it pushes the needle closed to cut off fuel flow and keep the bowl from overflowing. Once enough gas is used, the float lowers and the needle reopens to allow more fuel in. Neat! Until it gets stuck in the open position and floods, more on that later.


Here is a shot of the aforementioned float and needle system. In this shot, the float is moved up out of the way, as it would normally sit over the needle.


Taking all these tiny pieces off once again gives you an appreciation for the complexity and amount of development that must have gone into creating these Zenith 35/40 INAT carburetors.


This shot shows one of the main reasons I was doing the rebuild. The accelerator pump was pretty well shot on the rear carb. I actually now suspect that the little nozzle that sprays fuel into the barrel for the pump was just clogged, and that’s what was causing the issue where the pump would leak back due to the pressure caused by the blockage. Even after the rebuild we had issues with getting the pump to function correctly, so we back flushed the nozzle a few times and that solved the problem.


Neat little bit that, it works via the actuation of a small lever that you’ll have seen in pictures of the second carb layer. There is a piece of linkage on the top of the linkage setup that operates off a roller, when you hit the pedal the roller crests a lobe that causes that linkage to push the accelerator pump lever down. This creates the actual pump motion, and forces fuel into the barrel via the tiny nozzle in the barrel. You’ll probably have noticed that in other pictures as well. Pretty cool stuff!

Anyway, I made sure to clean everything up as best I could, and then got to putting it back together. Making sure you have the right gaskets between each layer can be tricky as each layer has multiple variations. It’s a game of matching every little passage with the gasket and making sure it all lines up right. I did end up messing the first-second layer gasket up on one of these and had to take it back apart later to put the right one in.


Finally, I made sure all the small surrounding parts were up to snuff by checking all the diaphragms and cleaning what I could. Then I reinstalled those on the main body.


Once of those little snap rings was a major pain, hard to get off as we didn’t have a snap ring pliers that went small enough, and thus I had to pry it off. I ended up using a tiny socket to smack it back into place, not exactly up to Mercedes-Benz standards, but it worked.


Unfortunately, one of the bolt holes had been smushed in slightly. I believe this happened when Sam was wielding a hammer with the intent of making things come apart. It was a small enough bend that we were able to run a thread chaser into it to correct the issue.


Some of the gaskets (that I’m fairly sure did exist when we took this apart) weren’t in the kit. So I made my own out of gasket material. Dad made the first one which I then used as a template for the others. I also decided to replace the cracked hose for the fuel supply between the carbs.


Once I had both carbs back on the manifold, I decided I’d clean the aluminum intake manifold since it was out of the car. Definitely should have thought of that while the carburetors where not attached. Another thing I should have checked is the exhaust riser flaps. These are known to rust into place and, if open, they can overheat the carbs and cause the gas to boil off or warp the aluminum bodies of the carbs. I was able to get them closed and wire them there after the fact, but it would have been easier while everything was off and in the workshop. Lessons for next time! Wait, there shouldn’t be a next time. Whatever, here’s how everything looked, ready to go back in the engine bay.


Nothing says “work in progress” like nuts and bolts scattered around the car.


Before I could put the manifold back in place, I had to clean up the gasket that makes sure things pass between the engine and the manifold without leaking everywhere. I’m pretty sure it does leak a bit anyway, that what I get for re-using gaskets! I just cleaned everything with a razor and brake clean, then applied copper exhaust sealant to help reduce the risk of intake and exhaust leaks. You can also see how well we did with making sure the valve cover sealant didn’t leak everywhere. Not well.


With that all taken care of, I put the manifold back on the engine. This, like taking it off, was not a feat easily accomplished. Naturally, I was on my own for this part. I jacked the engine up as I previously had, and then tried to line everything up and wiggle it all in to place. Eventually it worked, and I was rewarded with the pride that comes with seeing things all back together.


Some of the hoses that get attached in this area are a bit hard to work with as there isn’t much room. A coolant hose also runs past the manifold and was slowly rubbing itself apart on a rather sharp edge. Poor planning that. I put a new hose on, and cut part of the old hose apart to use as a second layer between the new hose and the sharp bit. That’ll give me some more time before it sprays coolant everywhere in a fantastic display.


We had some issues with the float sticking open on the front carb, so I had to remove the top two layers and poke it to make sure it would stop the needle when it was supposed to. Once it was unstuck, it stopped pouring gas all over the warm manifold, win!


Once we got that all figured out, it was time for some:

Exhaust Work

The problem: the exhaust resonator, muffler, and pipes were rusted pretty badly with holes is more than one place. I was able to locate a stainless muffler on Craigslist for the great price of $20. I also picked up some clamps, some reducers, and a straight pipe for where the old muffler had been. Sam helped me lay everything out and get a general plan for what we wanted things to look like when we were done.


When we had the general idea down, we started cutting out the parts that we didn’t need. Then we laid things out again to make sure that we were still on the right track.


Then Sam started welding, and I started watching. I can’t weld, not well anyway. We also only had our stick welder to work with, and it’s not great. Once we had done what we could, I got in touch with Matt and asked if he could help with the rest. He has a better wire welder, and is very skilled at using it.


Matt was nice enough to help me out, so I drove out to where his welder was and we got started. I basically told him what we were trying to accomplish, and Matt got it done. I owe him a nice supper.


There was plenty of welding to be done, and Matt also cut up some sheet steel to make a plate to cover some of the holes in the pipe. If I had the money, I would have just bought new pipe to run all the way back.


After grinding some of the welds that weren’t well done, Matt got to work forming the cover piece to weld over the biggest hole we had left. It took some hammering and welding, but it ended up looking nice and working pretty slick.


Then we had to make sure everything was lining up right and would come out fine. When we were satisfied with what we had, we started welding in the parts that would join the header pipes with the pipes going to the back.


By now, Matt had been working on this for a few hours, and we were finally to the point that it was good enough. I thanked Matt and promptly killed the car 3 times while trying to leave. This was before the new battery was in, so he had to jump me every time. Seriously, I owe Matt a nice dinner. Thanks Matt!

I tried to use some exhaust clamps to tighten things down but that didn’t completely work. I later had to cut them off with a grinder, polish things up a bit, and then cut up Bush’s beans cans and use a normal hose clamp to tighten it down after smothering it with exhaust concrete. That worked better than the exhaust clamps, but there are still some leaks. I also learned to always use anti-seize on bolts, since I broke almost all of them trying to take the clamp bolts off.


That’s all for this post, sorry it took so long! I’ve got one more post planned for this series, covering the water pump, brakes, and my second go at the valve cover gasket. See you then!


About Justin Marwitz

I'm the owner of this here site, and don't you forget it!


  1. Fantastic write up! Great story, great photos. Love this. Total immersion here, I have a metallic taste in my mouth right now. I’m kinda geeked out.

  2. how do you get the accelerator pumps out of the zenith 35/40 carbs ?

    • Getting the accelerator pump out is actually pretty easy! In the post I wrote up I referenced 3 “layers” of the carb. To get to the pump you need to take that first level off, there should be 9 or 10 bolts that need to come off for that to happen, including the middle bolt. This image shows pretty well the top “layer” sitting on the left and the second “layer” on the right with the pump visible near the bottom:

      You’ll also need to disconnect the throttle linkage so that you can freely actuate the lever that presses on the pump. Once that is done you should be able to move the lever out of the way and pull the pump straight up. Let me know how it goes, and thanks for stopping by!

  3. This is such a great site, Justin! I appreciate all the work you’ve put into explaining everything. I have a 1972 280 C (W 114) that I’ve been working on for a few moths and just got running this afternoon, only to discover gas pouring out of the front carb. A little research told me the float was probably stuck open, and I figured it was time to get it towed to the experts, since I didn’t think I wanted to mess with taking the carb apart. But then I was fortunate to come across your site, and your photos & descriptions have encouraged me to tackle it myself (and maybe electronic ignition next!). Thank you!

    • Glad to help! I had the luck of coming by my W114 very cheap, so I wasn’t too worried about if I broke something by taking it apart. Luckily, as difficult as these carbs are to perfectly tune or balance, they’re fairly easy to take apart and put back together.

      I’ve actually switched my 250 to a Pertronix ignition about a year ago now. It was a pretty easy switch and I feel that it runs more consistently after the swap, I’ve got a short write up on that as well ( Let me know if you need help with anything else, I can offer whatever advice/knowledge I’ve got!

  4. Hello Justin. Great write up. I am struggling a bit sourcing out a rebuilt kit for the carbs. I am finding kits from 50 to 200! Any recommendations on the brand and part numbers? Cheers evan

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