The following information is from a sheet I received from Doug Jackson
at British Automotive, Novato, CA (415-883-7200). He has a packet of
a number of interesting writeups on MGB performance, including info on
distributors, cams, carbs, heads and big bore.
The 25D distributor was used from 1963-74 1/2. The numbers include
40897 (63-65), 41288 (66-67), 41290 (late 67), 41288 (68), 41264 (69),
41288 again (70), 41339 (71), 41370 (72) and 41491 (73-74 1/2). The
vacuum advance units used were 54411985 (5-13-10), -2170 (5-11-7),
-5625 (5-11-8), -4868 (7-13-5) 54423989 (7-13-5) and 54435359
(10-15-5). The numbers in parentheses refer to starting vacuum,
finishing vacuum and advance, respectively. In other words, 10-15-5
means starts at 10 mm Hg, finishes at 15 mm Hg and advances 5 degrees.
(distributor degrees, multiply x 2 for crank degrees). Unfortunately,
there is no rhyme or reason to which advance was on which distributor,
this seemed to change on almost a monthly basis.
However, as pointed out by Randy, all dizzies through 1970 were ported
to the carburetor, and 1971-74 1/2 models were ported to the exhaust
manifold. I have no authoritative info on 45D4 units (electronic).
A. B. Bonds
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