Weber DGV Carbs on MGs | Bradley Restoration

Return Linkage Parts

Fri, 21 Oct 2011 09:54:33 -0700

If you don't have an old factory linkage to salvage the parts from, it is quite easy to make what you need.

Get yourself a piece of 3/16" round stock, 4-3/4" long, a couple of washers and a spring from the hardware store. Bend the rod 90 degrees, 3/4" from the end and drill a small hole for a cotter pin. The washers can be mounted by either tack-welding or even with a blob of J-B Weld, if you don't have access to any welding gear. I suppose you could make it out of brass and solder it, but I have never gone that route. Let me know how that works out for you.

Return Spring, alt. View

Fri, 21 Oct 2011 09:52:43 -0700

Just eyeball the location of the additional hole in the linkage. Try to keep it parallel to the cable and it will work fine. On a DGxV carb, it will be a mirror image of this setup.

Return Spring (DFEV)

Fri, 21 Oct 2011 09:52:34 -0700

Generally, Weber kits come with a little tab that goes on one of the exhaust manifold nuts, with a return spring to hang onto it. While it sort of works, it looks cheesy and often hangs up on other things and blocks access to the linkage and idle settings.

Here is what I came up with. (Pictured here is a DFEV, which is just a mirror image of a DGEV, mounted on a late Midget. A DGxV will be exactly the same, just reversed.)

I salvage the little arm and spring off of the factory Stromberg linkage and drill a 1/4" hole in the Weber cable bracket. Perfect geometry, clean and out of the way.

Just a Little Pinprick

Mon, 27 Oct 2008 18:08:09 -0700

There is a small orifice in the arm over the primary bore. There will be a number stamped on the nozzle, probably 50 or 55, which equates to .50 or .55 mm. We are going to open up this up to .70 mm, to give a larger shot of fuel under acceleration. This will get rid of the stumble.

Take the same #70 drill and open up the existing orifice up to .70 mm. The hole is at a slight angle, and you will feel it break through into the supply passage that leads down the arm of the nozzle.

Blow out any chips and you are good to go. Re-install the nozzle, with a crush washer on both sides. Re-assemble the bowl cover and your Weber will perform quite admirably on your MGB.

Successful Extraction

Mon, 27 Oct 2008 18:07:25 -0700

Here is the nozzle and its screw on the bench. Note that there are two copper crush washers in the assembly, one above and one below. Don't let them escape under the bench or anything. They need to be there or fuel will dribble out all over the jetting platform, instead of shooting down the bore as it should.

Over the Top!

Mon, 27 Oct 2008 18:07:10 -0700

Using the proper screwdriver, remove the 6 screws that hold on the fuel bowl cover, which is the whole top cover of the carb.

Depending upon which model you have, you will either have a cotter pin, hairpin, e-clip, or a slip-off rod connecting the choke mechanism on the body to the choke flapper on the lid. I will leave you to figure out which you have, but you will still need to disconnect the cover from the body.

Once you get the cover off, you will see this slotted-screw affair between the bores. Remove the large one and the cast fitting with the two little arms. This is the accelerator pump nozzle. The two brass screws are the air corrector jets for the primary and secondary main circuits. We won't be messing with these, as that is not part of the scope of this article.

I got it covered.

Mon, 27 Oct 2008 18:06:02 -0700

Once your hole is finished, be sure to blow out the chips.

Get your Loctite or JB-Weld ready. Put the slightest dab around the edge of the plug and press it back in. It should seat up against the existing shoulder. I smeared a bit of JB-Weld at the top edge, so that it can't move, but this is probably overkill.

(If by some chance, you buggered the plug when you removed it. You can still save things. Tap the bore 5/16"-24 and make a short plug out of a cut-off section of bolt, no more than a quarter of an inch long. Cut a slot in one end for a screwdriver, and install it in the threaded section with a dab of loctite. Be sure not to make it too long, or it will interfere with the mixture passage behind it. Good to go.)

I'm Fixing a Hole

Mon, 27 Oct 2008 18:05:37 -0700

Three little holes are we.

Mon, 27 Oct 2008 18:04:32 -0700

Here is where you will want to add a third hole.

Chuck up your #70 drill in the pin vise and get ready to drill. Eyeball the location where you will put the hole and give the drill a few twists. The drill will cut very slowly. Have a look at your start location and adjust accordingly. You can shove the drill around quite a bit before you are really committed. Once you are happy with your placement, start drilling. It will take about a minute to slowly drill all the way through. Use light pressure and keep the chips clear.

You can see that I started a bit higher and then moved to a lower position. In truth, anywhere in between this final location, and the mark left by my aborted start will be fine. The important thing is to aim carefully once the hole is started, so that it comes out in the right place. You are shooting for just overlapping the second, on the vertical axis, the way that the second hole overlaps the first hole.

In this case, I angled the drill upwards, only slightly, and it came out perfectly. See the next picture...

Making Progress

Mon, 27 Oct 2008 18:03:33 -0700

The two progression holes can bee seen if we peer straight down. We will be adding a third hole above the upper, smaller one.

The idle circuit gets a good vacuum signal in a very narrow range of low airflow, and is easy to adjust with the idle mixture screw. The main circuit gets its signal from a much greater amount of air flowing though the main venturi, and is tuned via jetting changes.

The progression circuit fills in the gray area that is just out of range of the idle adjustment, but before the main circuit kicks in. We are going to add a third progression hole to extend the range of the progression circuit.

I'm Looking Through You

Mon, 27 Oct 2008 18:01:36 -0700

... a hole, through which you can see wonders! Ok, maybe its not that exciting after all.

With the plug removed, you can see the progression mixture chamber and the passage above it that supplies the fuel/air mixture. And...

Target Acquired...

Mon, 27 Oct 2008 18:00:03 -0700

For the purpose of this demonstration, I grabbed a used DGV out of my parts bins. Please excuse the dust.

Here is the little plug you will need to remove, right above the idle mixture screw and the between the two vacuum ports.

Use your 7.5 mm drill and start slowly. Generally, the drill will grab the soft brass and the plug will start to spin. This is just fine. Keep it spinning and it will pull right out, leaving...

You will need...

Mon, 27 Oct 2008 17:59:02 -0700

If your Weber is already installed, you will need to remove it from the car with regular hand tools.

In addition, you will need to come up with a pin vise, which is a small hand-operated drill for holding very small drills, and a #70 drill, which is all but identical to a .70 mm drill. In addition, you will need a drill approximately 7.5 mm or a bit less. Letter drills M or L will work just fine. This is to remove a brass plug.

Finally, you will need some loctite cylindrical retaining compound, RC 620 OR some JB-Weld, or similar, chemical-proof epoxy, for when you replace the plug. (I have not found a place to buy plugs new on their own.)