Prior to jumping into the carb rebuild, I did some research on the internet about Weber Carbs, rebuilding, etc. There really is not a lot of how-to information on carb rebuilds. Thus I'm making more of an effort to document my experiences. A lot of the information here would be applicable to most carb rebuilds, so extrapolate as you wish.
The CX 2200 has a Weber 34 DMTR, which is part of the Weber two-barrel, progressive family. "Two barrels" because there are two barrels, and "progressive", because the throttle plates open progressively, not in unison. It is not until the accelerator is at least 2/3 down that the throttle plate in the second barrel opens. I am very impressed with the design of the Weber carb. It's a nice and elegantly simple unit. Given the complexity of the task, it has remarkably few moving parts. Most of the fuel metering is done with relative air pressure, not valves or needles with oil dampers. Click here to see an very good introduction to Weber Carburetors.
Here are some recommendations on rebuilding your carburetor. 1} STUDY, STUDY, STUDY. You really need to understand the theory of the Weber carbs before you jump into a rebuild. There are so many variations within the Weber families that you are unlikely to find a manual that addresses exactly your carb. However, this is not a problem if you have an understanding of how the circuits, etc. work.. I found that the DMTR was very similar, but not exactly identical to the carbs demonstrated in Haynes. All the principles of Weber carbs were there on the DMTR, but just in different locations. All of the components of the Weber carb were present on mine, just arranged differently from the carb rebuilt in the book. If you understand how carbs work in general , you'll be better able to understand your carb, even if it does not match what you are looking at in the book. If you understand the .principles, you can say "ok, here's the second circuit emulsion tube, even though the carb in the book has it in a different place." You're going to have to be able to recognize the idle/low speed, primary and secondary circuits, and accelerator pump on your carb, just by looking at where the fuel & air is ducted. you cannot depend on a book to show you exactly where it is. That being said, where to get information?
Several Sources: The Haynes Techbook. Haynes publishes an excellent book on Weber carbs, with thorough explanation on the theory and practice of their operation. Buy it and read it several times, even before you think about getting started. There is another book on Amazon that presents Weber carbs, but I did not think it was as helpful as the Haynes. The Haynes book does not address the DMTR specifically. However, you will find that the DMTR is part of a family of carbs, a member of which is rebuilt in the book. You will also need the Haynes shop manual specific to your car, as it will have some information on the specific carb fit to your engine. There will be diagrams showing the jets and emulsion tubes for your carb, and their locations. Pierce Manifolds I purchased my rebuild kit from Pierce, and I highly recommend them. Their website has exploded diagrams of all the carbs they support, and you will find these diagrams are infinitely valuable when you rebuild. They also gave me technical advice over the phone on several occasions. Even if you do not use it, it is nice to know that there is a resource there - if you come across something you do not understand, they can talk you through it. Excellent before & after sale service. Here is a .pdf of the DMTR exploded diagram
Shane, in Australia, did an excellent documentation of the rebuild of his DMTR carb. The information here is meant to be a adjunct to what he has already accomplished so well.
2} A WEBER Rebuild is not really a "rebuild". It's really a thorough cleaning. The elegant part of the Weber carbs is that they have very few moving parts. Fuel metering is determined by the internal passages and the holes on the emulsion tubes, not by complicated valvings & junk. So, what for other carbs is a rebuild, for a Weber, it's just a good scrub. The primary moving parts on the Weber carb are the shafts that open and close the throttle plates. In several places (Haynes, Pierce Manifolds) I was told NOT to touch these shafts. They are very precisely set in the carb body, and removing them risks grave damage. If the shafts are so worn that they are REALLY leaking air, you are better off buying a new unit. The risks of misassembling the shafts far outweigh the benefits of taking them out for a cleaning. If they function smoothly, then give the areas a good cleaning, and hit them with some lithium grease. So, most of your work will be with toothbrushes and carb cleaner, rather than wrenches and screwdrivers. There are components that you will detach from the carb, but many of the mechanisms will stay in place. The throttle plate shafts can be cleaned, checked for range of motion, and lubricated without removing them the body. If you can do all of this with the shafts in place, then by all means leave them there.
3 A shopping list:
Disassembly: MOST IMPORTANT: Relax & take your time. If you rush, you are likely to lose parts, or miscatalog something. Think of the process as an assembly line. A part comes off the carb, goes through the cleaning process, and ends up properly catalogued for reassembly. NEVER have more than one part off the carb at one time. That way, you'll never be confused as to what it is or where it came from. This is most important when you are taking out the jets and emulsion tubes. It you mix these up, you am be seriously fukt. When the part comes off the carb, put it in a wire strainer, put the strainer over a juice glass and blast the part with carb cleaner. Use the juice glass to collect the carb cleaner fluid. You will soon have enough in the glass to soak the parts. Some parts will have a lot of gum and garbage on them and they will need a good soaking. The jets and emulsion tubes need special care. Soak them, blow air through them, but absolutely DO NOT POKE ANYTHING IN THE HOLES. The holes are positioned and machined to meter the fuel/air mixture exactly. Location, diameter and angle are all very important. If you poke things in the holes, you will probably alter diameters, or scratch a bore or something. You might say, "But I'll be gentle." No. Just soak & blow through with air. The jets and emulsion tubes will come apart, which helps in cleaning. Again, only one off at a time lest you not mix them up. Each part of the carb has an associated number on the diagram and the parts list. While the part is soaking, write down the part number and the name on the paper cd sleeve. During the soak, look though your bag of new parts in the rebuild kit. If there is a new replacement part, put it in a sleeve. Different color sleeves are very helpful here. I used fluorescent orange and green (cool colors for hip music thieves!!) I used orange sleeves for old parts and green sleeves for new parts. The sleeve with the new part gets stapled to the sleeve with the old part. When you reassemble the carb, you will be VERY HAPPY you took the extra time to do this. After the soak, scrub the part with the brush, and dry it with the air. Put it in the sleeve. If there is carb cleaner on the part, it will melt the plastic window of the CD sleeve. No worries, carb cleaner will take it right off, but you don't want to clean it twice. Some mechanisms will come off the carb and need further reassembly. The accelerator pump is a good example. After you have completed the disassembly, stop & take a break Reassembly: Do not start reassembly until you have completed the disassembly and cleaning steps. And, please, take a break before starting the reassembly. You want to be rested and have a clear head when you start. The reassembly will go quickly and smoothly. Because you took the time to catalog the pieces as they came off the carb, you will remember how they are reinstalled. The value of referring back to the exploded diagram and writing part numbers on the CD sleeves is that you stopped and thought about each part, where it came from, and its name. These three things are immensely helpful in reassembly. There is no instruction book to tell you how to put the thing together. When you start, you will have a stripped carburetor body, and a set of CD sleeves with parts. Screen to minimize clogging of the jets and passages.
|