Summitt has a new carb. It looks like a cross between a Holley and Autolite. $250.
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This carb looks to be excellent, it has all of the right features and the adjustable idle bleeds are very desireable in that they allow adjusting the transition circuit (and 90% of street driving is on the transition circuit). A further plus is that the carb is made of aluminum, not zinc. Aluminum is real metal; when is the last time you saw zinc cylinder heads?
But there is one very important problem. Because the power valve is on the botttom, Summit says that a 1/4 inch spacer is necessary between the carb and manifold. The spacer is included with the carb, but with a stock MGB hood it probably means that an air cleaner will no longer fit in most cases. I would have tried this carb, but the spacer requirement means it will not fit on my car.