We know that the balancing of SU carburetors requires the removal and replacement of the anchoring nuts and bolts, and washers for the air cleaners. We also know the contortions required to replace the washers and nuts up under the carbs (as well as the kneeling, searching and cursing when we drop them...twice!). I think the following might simplify the problem.

The holes in the carb flanges that the 1/4" (.250") air cleaner anchoring bolts go through are .257" plus (at least the ones for my BN-1 Austin-Healey "H" carbs) and this just happens to be the recommended hole size to install 5/16" x 18 t.p.i. helicoils. Run the 5/16" x 18 t.p.i. tap in a helicoil kit into these holes with the wing nut tool. The insert may be a little long for the thickness of the flange but screwing a 1/4" x 18 tpi bolt through will break off the little tang and set them.

Now the removal and replacement of the air cleaners is from the outside, and washers and nuts under the carburetor are not required. This method can also be used on other British cars with the same set-up.

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