DMSA Rebuild

[aj81spider]

So I have a new head being built and the car is down for 4 weeks until it gets here. Before it the head came off the throttle responsiveness was not great and a carburetor rebuild had been in the cards. I decided to bite the bullet and do it now. No questions in this post, just my experience doing rebuilding it. The car is a 1974 and the carb is a DMSA 34 100.

Before pictures - it was pretty filthy (inside too as it turns out):





My advice is to take about 10 times as many pictures as you think you need to. Basically take a picture of every screw, spring, and lever you take off, as you take it off. I also was out of plastic bins (too many things disassembled right now) so I put a giant piece of paper on the floor and boxed out each thing I took off the carb. I took notes and called out the box on the paper for the screws/nuts etc I took off.



I also took a lot of pictures like this - where the things that came off a shaft were laid out in the order they came off.



I'd never rebuilt a carburetor before, so I moved slow.

It took me about 2 hours to disassemble everything. Then it took three evenings to clean it all. I bought a gallon can of carb cleaner and soaked the body and some of the jets. It turned out that the shafts and levers and small body parts actually cleaned up easier with my wire wheel. Cleaning everything was definitely the longest step.

I had a couple of rebuild kits. The main one I used was a full rebuild kit that I was only able to find from Chris Obert. It was pretty good, but there were a few things that I got out of a couple of other kits I had. My big complaint is that none of the kits had the cotter pins used to hold a bunch of stuff together. Mine were 40 years old and several disintegrated.

Most of the jets were the stock jets, but a couple weren't. I set everything back to the factory jets, figuring that would create the best baseline for tuning the engine after reassembling it.

Here it is reassembled. I won't know if it works for a couple of weeks, but it looks a lot better!

[ScotcH]

This is very timely ... I have 2 of them, one to rebuild, the other as a "you idiot, this is what it's supposed to look like" Will be doing it after next weekend, so I might be asking for advice if I run into issues.

And while I'm here, a couple questions for you (or anyone else with a DMSA):

- is the DMSA returnless for fuel? I currently have only a supply line and it would suck to have to run a new line back to the tank
- Can I plug ALL the nipples other than the fuel? Again, that's what I have now ... just fuel line, that's it ... no emissions of any kind, no choke, no vac advance.
- Mine is going on a 78 1800 ... I, like you, want to get back to a known good baseline.

[vandor]

Yank hard on the fuel inlet and outlet nipples, to be sure they are secure. They have a tendency to fall out and then fuel sprays everywhere. I have converted a few carbs to threaded barb fittings.

[aj81spider]

Csaba, where do you get the threaded barb fittings (and what size)? One of my fuel connections (the vent I believe) has fallen off. I tried to spread the end a bit and tapped it back in, but now is a good time to convert them since the carb is out of the car.

ScotcH to answer your questions - mine has three connections: Fuel in, return, and a bowl vent. Here's a picture of the three lines hooked up. I think (but don't completely trust me on this) that the bottom front is fuel in, the top front is return, and the back one is the bowl vent. The hoses connect to three hard lines that run back into my trunk.



There are two vacuum nipples on either side of the idle adjust screw. Those are plugged. There's also a large nipple in the back that my diagrams say goes to the fast idle diaphragm. That was open, but I plugged it just to keep dirt out of it.

I have lots of pictures if you run into trouble (but as noted above, less than I should have taken!).

One tip I will share - the hardest part of the job was getting the spring on the choke adjust lever back on. It has to be wound pretty tightly and the lever just sits on a boss waiting for a second lever and screw on top of it. I spent a lot of time trying to get it on. What finally worked was to assemble it with the spring in place but not connected. I tied a piece of string to it and snuck it around all the levers. Pulled the spring end tight and it snapped right on.

[vandor]

The fitting is available at some hardware stores. I think one end is a 1/8" pipe thread, the other is a 5/16" barb for the hose.
One must tap the hole in the carb for the pipe thread.

[ScotcH]

Ok, rebuild done, but I have some questions:
- There are a bunch of left over rubber O rings from the rebuild kit (4 I think) ... I only used 2 on the side screws (idle jets??) Are these extra, or did I not disassemble something?
- There were 2 very small tubes (about 2mm diameter, 4mm long) that came from the top of the carb after I took off the top. They seem to go in the small holes around where the emulsion tubes and the jet pump nozzle is bolted in ... What are these, and which of the 4 hoes do they go in? Want to confirm I have it right
- What's the big nipple for on the square diaphragm looking thing with the adjuster screw on top. Can I plug that, or where does it go?
- Is there a diagram of this thing that has English labels so I don't have to describe the parts, and just call them by name? In the Italian diagram, that diaphragm thing is called "capsula" ... so capsule. Very descriptive, lol
- Where are there markings on the jets and other bits? I see the F7 on the emulsion tube, but can't seem to any any other numbers, except 175 on the needle valve (and 200 on the new one in the rebuild kit).

Thanks in advance!

[aj81spider]

Here are my answers as best I know. Major proviso that I don't really know what I'm doing, but I simply took a lot of pictures.

There are a bunch of left over rubber O rings from the rebuild kit (4 I think) ... I only used 2 on the side screws (idle jets??) Are these extra, or did I not disassemble something?

I'm not sure what the correct number is (my kit's got mixed up but seemed to have a lot more than 4). However I do know of two other o-rings. One is on the idle mix screw, the other on one of the assemblies that mounts to the side of the carb.

There were 2 very small tubes (about 2mm diameter, 4mm long) that came from the top of the carb after I took off the top. They seem to go in the small holes around where the emulsion tubes and the jet pump nozzle is bolted in ... What are these, and which of the 4 hoes do they go in? Want to confirm I have it right

I don't know what they are called, or what they do. However is a picture. One of mine stuck in the top and one stayed in the bottom.

What's the big nipple for on the square diaphragm looking thing with the adjuster screw on top. Can I plug that, or where does it go?

I have a diagram that calls it the fast idle diaphragm. The nipple was unconnected on my carburetor when it was in the car (I think it is normally attached to some of the emissions stuff - but am not sure). I plugged it just to keep dirt out.

Where are there markings on the jets and other bits? I see the F7 on the emulsion tube, but can't seem to any any other numbers, except 175 on the needle valve (and 200 on the new one in the rebuild kit).

On mine some of the numbers printed on the sides, some on the top. They are etched into the metal and you have to clean them really well to see. I used a wire wheel and got them shiny.

[ScotcH]

Thanks for the info! Got it all back together ... but my accel pump diaphragm is leaking I did not get a new one In the rebuild kit for some reason. Trying to source one quick.