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MG Midget and Sprite Technical - Weber Carb Troubles

Hi All,
Have a '75 1275 with a Weber 32/38 (I Think) DGV carb. Has been on the car over 10 years. It has always sputtered when transitioning but is now much worse. The small barrel seems not to get gas. Runs great once I get the 2nd barrel opened up.
Any ideas?

Thanks,
Jim
James Porter

Jim. Time for a through cleaning and rebuild. The new rebuild kits, by EMPI contain more parts than the older Weber kits (which are no longer being made, but may still be on the shelves). At the ten year point, you will need to replace the power valve and accelerator pump diaphragm, both of which are included in the new kits. Take the air filter off the carb and operate the throttle. If you are not seeing a stream of fuel being shot into the primary venturi, the accelerator pump is bad. While looking, look at the two brass pipes going across the tops of the venturi. I have seen these pipes back our, causing erratic fuel flow. They are enclosed on a zinc or aluminum piece which lifts out the top of the carb.

After ten years, especially if the car is not a daily driver and fuel sits in the carb for long periods, some of the small passages inside the carb can become closed up. A through cleaning and installing the rebuild kit can bring it back to life. Pat Braden's book, "Weber Carburetors" works better for me than the Haynes "Weber Carburetor Manual", but each has their use and may explain something a little differently so that it makes sense to you. Not a difficult rebuild if you get a large piece of cardboard and lay the parts out in a logical order.

Les
Les Bengtson

Thank you Les,

You hit the nail on the head. When I operate the throttle, the fuel does not pump into the 1st barrel.
You are correct, the Haynes "Weber Carburetor Manual" leaves some to be desired. I will disassemble and rebuild soon. Thank you.

Jim
James Porter

Jim. No problem. I have the DGV on three cars--two of my own and my daughters. They are allowed as a replacement carb by our emissions inspection program. Hence, I have had to learn a little about the Weber DGV. One of the things I have learned is that Holley made a version, under license from Weber, called the Holley 5200 and it was used on several performance oriented cars. The DGV is not just an "economy carb" if you are willing to take the time to understand it and do some experimenting.

One design deficiency, at least to me, is the power valve. The power valve comes on to add more fuel when there is low manifold pressure--as when one accelerates. Unlike the accelerator pump which only gives "one shot" as the accelerator is fully opened, the power valve continues to provide a richer mixture (for more power) until the manifold vacuum increases back to its normal, steady state.

The problem, as we found with one of my cars which was failing emissions for high HC (unburned hydrocarbons) is that the high vacuum in the intake manifold is applied to a thin, rubber diaphragm which pulls the power valve plunger upwards against spring pressure. When the vacuum is not sufficient to overcome the spring pressure, the plunger is forced downwards by the spring, opening up the power valve which sits at the bottom of the fuel reservoir. The problem is, when the diaphragm gets old and ruptures, the spring forces the plunger downwards and the power valve is on all the time, giving a constantly too rich mixture--wastes fuel and causes poor running.

This is the rod and spring that sticks down into the fuel reservoir and is attached to the top cover of the carb. Make sure you change that part out when you do your rebuild.

Good luck. Les
Les Bengtson

This thread was discussed between 04/07/2008 and 05/07/2008

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