Rebuilding Stromberg Carburetors

By: Green Country Triumphs, Tulsa, OK

I thought that I would share a few observations about a typical rebuild. I do not claim to be an expert but having rebuilt several sets with reasonable success, I thought that passing along some of my experiences my help belay any fears associated with tearing into your own.

GETTING THEM OFF

Easy. First, the choke cables are attached to the choke mechanism by two cables pinned by two screws. Loosen the screws, then pry off the two retaining clips at the top of the carb. The choke cables are now loose. NOTE: I have removed more than one set of carbs where the retaining clips were missing and makeshift methods of attaching the cables were used, usually not very successfully.  Start a parts list now and if your clips are missing put them on the list. They are cheap. Ordering rebuild kits, etc. before the teardown is better avoided if possible. You really don’t know what to order until the teardown is complete.

 

The next thing to remove is the fuel line and other rubber hoses. One thing to note is if fuel flows through the fuel line via gravity flow you probably need a fuel pump rebuild or a new pump.  Sometimes the fuel pump can fail and the car still run, at least till you park on a hill or get down to about a quarter tank of gas.

 

Next to the firewall, the linkage attaches to the crossbar lever with a funny looking clip. Push the linkage out of the clip. It is that simple. It is usually harder to find the clip if you drop it than to get it apart. The linkage comes off with the carbs which are better removed at the same time by removing the eight nuts holding them to the intake manifold. Remove the two carbs keeping them upright because they still contain gas and oil and set them on a suitable work surface.

 

TEARDOWN

 

Before removing the linkage, study it. This is the simple key to recognizing the front carb from the rear carb. Keep the components properly segregated as front and rear until they are back on the car.  Some components are not interchangeable and do not work properly if switched between carbs.

 

After becoming familiar with the assembly, loosen the outside bolts of the linkage sub-assembly so that the carbs can be separated from the linkage and set the linkage aside for the time being. Find something to empty the remaining gas and oil into, then pour it from the vent port that feeds the charcoal canister. Remove the dash pot damper and pour the oil out.

 

I always tear down the front carb first because it is easier to make an F than an R. Sounds dumb, huh. Let’s proceed. Got your parts list? Keep it handy.

 

The order of disassembly really doesn’t matter but to explain the F – R statement above we will start at the top. Remove the four screws holding the dashpot on. Don’t worry, nothing will jump out, but there is a big, weak spring under there that will come out first. Put it in whatever container you have designated for this carb. The springs are interchangeable but you might as well start off right keeping everything separate.

 

You now have the dashpot (top) off the carb. At this point I use a scribe or nail to scribe an F on the underside of the piece. That way if the parts are somehow mixed up I can get the part back on the correct carb.

 

AIR VALVE

 

The next thing to take out is the air valve assembly. It lifts right out of the carb body. This should be done with some care so as not to damage the metering needle in the bottom of the air valve.

 

The attached diaphragm will be replaced by a standard component in the new carb kit so if it is torn or not very flexible it is subject to replacement anyway. Remove the four screws in the diaphragm retainer and separate from the air valve. Be careful of the metering needle.

 

Next, look at the metering needle. If you can detect wear on the needle, or if the mixture adjustment is such that the car runs rich all the time, you may want to replace these. The experts tell me that one of the worst things that can happen on these carbs is for the hole, in which the metering needle inserts, to become enlarged. This is one of the most difficult problems to fix and will probably require an expert. I will also say that I have yet to encounter this problem and to wear out a carb to this extent is most unusual.

 

Now, I like to replace the O ring which retains the oil in the damper. This O ring is not part of the standard kit so if you intend on doing this, put it on your parts list. Let’s finish the air valve disassembly. If you have adjusted your air/fuel mixture on your carbs you have a special tool used for this purpose. Get it out or add this tool to your parts list. They are not expensive and you are going to

need it.

 

Use the tool to separate the metering needle assembly from the retainer by inserting the tool and turning it counter clockwise until the needle assembly stops it’s outward travel which means the threads have disengaged. Then loosen the grub screw that keeps the needle assembly from turning in the air valve. Do this with care because I have ruined a grub screw and getting them out can be a real challenge. Typically they are not a problem if a little penetrating oil is used prior to trying to move them.

 

Once the grub screw is loose and the retainer is separated, the metering needle assembly can be removed. Do this with care as the needle assembly can be damaged if improperly handled. What is left in the air valve is the retainer which is little more that a short screw with an O ring groove. The retainer is pushed out from the bottom. Do not use something sharp as the retainer can be damaged.  It may not move easily, but it will move. Push it out, but don’t loose it. This is a good time to scribe an F on the bottom of the air valve so that they don’t get mixed up. The air valve is now disassembled so set it aside for now.

 

FLOATBOWL

 

OK, grab the carb body and turn it upside down. Remove the plug in the center of the bowl.

 

Replace the O ring in the plug before replacing the plug in the bowl. Remove the six screws holding the floatbowl on. There won’t be any surprises here so proceed with confidence. Once the bowl is off, pry off the floats, hold them up to your ear and shake them. If you hear gas sloshing around add floats to your parts list. Remove the brass colored jet in the corner and discard. A new one will be in the kit. I personally have no preference whether the new jet is a Gross jet or the standard type. They both work. Put the F inside the float bowl on the bowl and the carb body to identify the front carb.

 

CHOKE MECHANISM

 

Remove the two brass colored screws holding the choke mechanism on and set it aside. I have yet to encounter a faulty choke mechanism other than being dirty so no problems are anticipated here. It can be disassembled further I you wish but my experience says this probably is not necessary.

 

TEMPERATURE COMPENSATOR

 

Remove the two screws and washers holding this little piece of magic to the side of the carb. It is the assembly with the plastic cap about two inches long on the forward side of the carb.

 

At this point it is not necessary to remove the plastic cover. Check out the component by first pushing the plastic plunger to see if it moves freely. If it does not move, it will require disassembly and

cleaning. Scary, ain’t it.

 

If it does move, make sure it seals by trying to blow air around the seal. It should hold at least a small amount of pressure. If it does not seal you still have to do the scary thing. Remove the two screws holding the plastic cap on. Remove the lock nut securing the bi-metal strip. Remove the strip and the plunger and clean the assembly components as well as you can prior to reassembly.

 

Since this article is getting long, I will only say that if the instructions for adjusting these things are published by the VTR. It is not hard and it is not magic.   Look elsewhere in this list for those instructions.

 

MIXTURE TRIM SCREW

 

Take it out, clean it, screw it all the way in upon re-assembly.

 

IDLE BYPASS VALVE

 

If it has been a while since these things were overhauled the diaphragms are probably hard as a rock. They are the funny looking assembly on the forward side of the carb right next the brass colored throttle shaft. Remove the assembly by extracting the slotted screws.  Once the assembly is removed, extract the Phillips head screws.

 

Just to let you know there is a spring inside so don’t be surprised if the thing pops apart. Please note that the diaphragm has a gasket on both sides. When you re-assemble this unit put it back the same way or the diaphragm will not be properly supported. Moving the adjustment screw should be avoided if possible. Getting these things back into adjustment can be a chore.

 

This diaphragm is not part of a standard kit, so if you want it put it on your parts list. The gaskets usually are part of the kit. Go figure.

 

THROTTLE SHAFT

 

Last Assembly. See, not so hard so far. The hardware holding the throttle shaft in is on the aft (back) side of the carb. The front carb has a little different hardware than the rear carb so at to accommodate the linkage attachment. The round end cap is secured by a captive retainer bent up to prevent it’s coming loose unintentionally. Bend it down. You can now remove the end cap, specially designed washers and spring which closes the throttle.

 

Now remove the throttle plate by extracting the two screws holding it in. I suggest you add two new screws to your parts list. Depending upon the type of screw you have, they are either peened in or spread apart via a slot in the screw designed for that purpose. By spreading the metal in one of these two ways they are less apt to come out and be swallowed by the engine where bad things happen.

 

You can now extract the throttle shaft and examine it. I have never done a rebuild without replacing the throttle shafts. I can also say that I have never had to bush the throttle shaft holes. The shaft seals are normally adequate to assure a good fit that will not leak air. Brass retainers that pry out with a screwdriver retain the shaft seals. You might as well add these seals to your parts list because some kits have them and some don’t. The rubber is cheap. It is the brass retainers that get expensive so be careful when removing them.

 

Except for the small difference in the hardware for the throttle shaft linkage, teardown of the rear carb is the same process as the front. Now you have to figure out how you intend to clean everything. Fortunately for me, my good friend Sam Clark keeps a bucket of parts cleaner around that we use to clean members carbs. This is volatile stuff so we make one bucket do for both of us.  There are other more tedious ways to clean carbs which involves tooth brushes, pieces of wire, dremel tools, etc. which must be used if soaking is not an option. This is OK, it just takes longer and is more work.

 

Once cleaned, buffing of external parts is your option, but they sure look better. At this point the hard part is over. Re-assembly is a no brainer but there are a few things to be careful about.

 

The front throttle shaft may be longer than the one you took out. I cut them off. You do what you want. When you put the throttle shaft seals back in, just flush the brass retainer with the carb body, and don’t force them in as far as they will go. Lube the shaft so the new seals are not damaged upon insertion. This is a standard practice appropriate for many applications. The screws retaining the throttle plate must be set with a punch or spread apart, depending upon the type of screws they are, so they will not work themselves out.

 

Holding the carb upside down, the highest point of both floats should be .625 to .672 inches from the float bowl sealing surface. I use a pair of 6-inch calipers to make this adjustment. Some kits come with a cardboard gage.

 

When installing the metering needle, adjust the base of the needle to be flush with the bottom of the air valve. This is about the middle of the adjustment range and provides an excellent starting point for final adjustment. Of course, use all new O-rings and gaskets provided in the kits. Make sure to use both seals on the Temperature Compensator.

 

Make sure to line up the diaphragm seal tabs with the corresponding slots in the air valve and the carb body to properly set the metering needle bias direction. If this makes no sense, trust me. The tabs on the diaphragm fit into small slots. Just make sure they are in there. Also make sure the diaphragm is properly seated in the carb body so that it is not pinched and damaged when the dashpot is re-installed.

 

One last note on linkage. It is amazing how many cars are adjusted so that the carbs do not open all the way. Before you reattach the linkage to the cross shaft lever, push down on the linkage between the carbs to see how much travel you have available. Then hook up the linkage, operate the gas pedal and compare the amount of actual travel with potential travel. If you want to open the carbs more, adjust the length of the throttle rod which attaches to the cross shaft lever. This is done by loosening the set nut, then moving the long nut until optimum opening is achieved. Then re-tighten the set nut.

 

If the slot that the linkage travels through is worn, consider new parts here as well. This stuff can bind up and cause all kinds of problems. Also, put a drop of oil on the long spring on the linkage. If you like the space called for when adjusting the linkage put it in, otherwise don’t. I have not found it to make much difference one way or the other. Reconnect all the lines and hoses. Prime the fuel pump and add oil to the dampers. What kind of oil? The experts say whatever you use in your car is fine for the dampers. Everyone seems to have their own preference. I use 20/50W Castrol, like in my car. I am sure your way is better, so use it.

 

Attach the choke cables at the screw. Push the choke home to rest on the stop and push the retainer into position. This is the easiest way I have found to adjust the choke cables.

 

To you beginners this may sound difficult. It is not. To you guys that have done this before, your experiences are probably different from mine. I still think that it is important to share what we experience so that we can learn from each other. Good luck on your project.

 

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