TRIUMPH TR2&TR4A engine,...DCOE 40,42,45,and 48 all share the same basic construction,They all take the same jets,brass fittings and gasket set. The chokes, auxiliary chokes, horns & butterfly's and throttle shafts are unique to each carburetor size, and are not interchangeable between sizes. the 40 and 42 share one choke design(they look the same even though the outside diameter is different).The 45 & 48 share a common design, visually it is easy to confuse these parts without a trial fit. (note...Only U.K. built factory TR4 Rally cars were built with WEBER carburetors).Check these websites for the carburetor settings for your TR4...www.tr3a.info/weberDCOEinfo.htm and www.englishparts.com/triumph/tr4-tr4a/carburetors.

In a Weber book I found settings for a 40 DCOE 18 on a TR4 which I hope to use. The two websites you listed were not found when I tried them.