From the MGA Special Tuning Manual (for pushrod engines):

Tuning with high-compression ratio 10.0:1 and larger carburetors
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Fit 1 3/4 in. (44.45mm) dia. SU carburetors ....
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To prevent vibration of the carburetors it is advisable to use a synthetic rubber gasket (Part No. AHH5791) between the carburetors and the manifold and a 1/8 in (3.18 mm.) thick double-coil spring washer under the carburetor fixing nuts, so that the carburetors may be left not quite tightened solid. Wire the nuts in pairs to prevent them becoming slack.

At 10:36 AM 5/12/05 -0500, John Barber wrote:
>"I have a set of them and initially put them on. The problem is that the spacers move the carbs too close to the inner fender for the air cleaners (new original type from Todd Clarke). The front carb air cleaner rubs on the inner fender. .... I am watching for signs of the vibration causing a problem in the float bowl and leaning out the mixture and debating whether to reinstall them and go to some other type of air cleaner."