This MGA Twin-Cam is a car we have known and serviced for many years. The car was fully restored by the owner to a very high standard over twenty years ago, and has been an amazing car for him until recently when he started having a few running issues. We decided it would be best to fully rebuild the carburetors to new specification, and once again return them to show quality. The SU carburetors were rebuilt by us, as we have done hundreds over the years. The SU carburetor is a very simple carburetor, but like any other carb, needs to be rebuilt and adjusted correctly for the car to perform as it should.
Installing the carburetors on a MGA Twin-Cam is a little tricky, as they don’t leave much room to squeeze everything in, but once installed, is just like setting up any other SU carburetor. It is very important when adjusting these carburetors to make sure the air speed is exactly the same on both carburetors before going too far into the carburetor adjustment. This is quite easily achieved by using an air speed meter and disconnecting the carburetor linkage so that the carburetors can be adjusted separately. Once the air speed is set, things get a little more difficult as this is where we adjust the mixture. There is no right or wrong way to do this and it can take some time. After doing this for so many years, we have a feel for what the correct air fuel ratio is and what is not.
At the end of the day, we got this car running just like it did over twenty years ago when it was restored. When working on any of these old cars, it is very important to remember that the fuel we use today is nothing like what was available when these cars were new, so the best way to adjust carburetors and ignition timing is by trial and error.