CB-101 is a quick review of a variety of carburetors you might find on the MGA. The MGA Twin Cam used SU H6 carburetors (mounted on the opposite side of the engine). All other MGA used SU H4 carburetors, and anything you else noted here would be transplanted aftermarket parts.

Original type SU H4 carburetors

All MGA (except the Twin Cam) used twin SU H4 carburetors with 1-1/2" throat size. These had the float chamber on the side (as shown above) and might have a minor fuel leakage around the main jet on the bottom.

MGB from 1962-1971 used SU HS4 carburetors. These are similar to the H type, but have a small hose on the bottom connecting the float chamber to the main jet, which effectively circumvents the jet leakage problem.

The MGB from 1972 to 1974 used SU HIF4 carburetors. These have the float chamber in the base of the carburetor, the bottom of the carb is square, and no float chamber on the side. So far any of these can work okay on the MGA.

The 1975-1980 MGB used a single Zenith-Stromberg carburetor mounted on an integral cast iron manifold incorporating intake and exhaust, and connecting to a catalytic converter. This is the worst of the worst (performance wise), and you should hopefully never see this on any MGA.

Occasionally you find a Weber two barrel downdraft carburetor on a matching intake maniflod. This is generally functional, just no so cool, may give better starting and driveability with a slight loss of top end power. This would usually be done in a prior life when the original carburetors might be worn out, or missing, or when some misguided soul was convinced the the word "Weber" would make the car go faster (or at least be more impressive).

If someone was a performance enthusiast, you might find dual SU H6 or HS6 or HIF6 carburetors, which are similar to the #4 counterparts, but having 1-3/4 " throat size and a 4-bolt mounting flange. If nothing else is modified, such an increase in throat size may do very little for performance except for a minor improvement in torque at engine speeds above 5000 rpm. You might also get a minor drop in torque below 1500 rpm, possibly a slightly rough idle, and maybe a little loss of fuel economy. For good effect the larger carbs should be accompanied by some porting of the cylinder head, or possibly a change of head with larger intake valves and better porting, and possibly a better exhaust manifold or tubular headers.

If someone was a maximum performance nut, you might find a Weber dual side draught carburetor, which has the potential of giving good top end power, but can be difficult to tune for reasonable performance in daily driving conditions. These may not be much different than the SU carbs for top end performance. A Weber 40DCOE (40mm throat) would be close to the SU #4 carbs, and a Weber 45DCOE would be close to the SU #6 carbs in performance. Flat out racers may prefer the Weber for a small edge on far top end performance. Vintage racers may perfer the SU for appearance and ease of tuning.

Weber 45DCOE side draught carburetor

In time I hope to get more pictures of each of these options to post here.