there might have been, the tag is pretty scuffed so I can't really tell

AUC 1390 isn't in my book....let's wtart thinkinh what other brands of cars besides BL used SU carbs....Volvo? Mercedes?

Tony - AUC 1390 is the part number for the float bowl. Every component has a part number and it can be used on many different carbs. The tag on the float bowl cover is the part number for the complete assembly.

That's true but I didn't find it in on my list of SU carb parts....found all the needles in various carbs, but no AUC 1390.

Item # 994

So, in what car is an FZX 1253 carb used?

My catalogue shows that an FZX 1253 is an HS2 used in a single carb configuration, from 1976-77 on a Reliant ROBIN/KITTEN.

Well, now, that's pretty interesting....didn't the Robin/Kitten use an A Series engine?

Interesting - I can't find an engine picture online - seems like a lot of conversions though. It was an 848 cc engine thus not likely A series

Reliant built their own, very fine, pushrod OHV all-aluminium angine, to replace the sidevalve 750cc they'd used for years and was a re-vamp of the Austin Seven engine.
Originally the new engine was 597cc (I had one once, a long time ago) which over the years grew to 848cc.
FYI, the engine became the replacement for the Austin Seven in the 750MC 750 formula, originally alongside the Austin engine, and today with the Fiat Fire.

Note- the Mini "A" type was also 848cc.