" This lovely little 250 is owned by a friend of mine who asked me to ask a few questions on his behalf "
____ He's more than welcome & ought to join-up with us (for direct interaction with this w.site).
" It has the SS1 29 carb, high compression piston, a very "hot" cam
and kit megaphone fitted "
____ The non-stock carb (& other of such) may perhaps be from an installed factory race-kit, Or a previous-owner may have tried to emulate such.
" The engine number prefix is DM250 rather than DM250M3. It is unclear to me from my reading if the early Diana's exported to the US had the M3 notation "
____ I'm quite certain that the suffix 'M3' was not included on any 'Diana Mark III' motor before the '250Mach I' model went into production for the 1965 model-year.
" How do these numbers sit with it being an original 64 Mark 3? "
____ The given motor-number is fairly consistent with the 1964 model-year.
However all publications I ever recall refer to the specific name as 'Diana Mark III' , not "Mark 3" !
" It's not even clear to me from my reading when the "Mark 3" name became "official") "
____ I've discussed this particular issue once or twice before...
__ I recall seeing mag.ads by the U.S.importer -('Berliner'), which even after the 1964 model-year, continued-on referring to the 'Diana' name for the 1965 & 66 250 Mark-3 models. _ But certainly by the time the w-c.250 Mark-3 models came-out, the Diana-name had become officially dropped.
So the importer much contributed to the blurriness of exactly when the model-line actually got it's name officially changed to simply "Mark 3". _ Some old Duker in Italy ought to still be aware of the exact year when the name-change ACTUALLY took effect officially by the factory.
However I surely expect that the owner's-manuals from all the years that model-line was produced would certainly help clear-up the issue. _ I say "help" because I happen to know that the factory was not very careful to exactly match-up owner's-manuals precisely to the particular model-year, from year change-over to year,, (in other-words, your brand-new 1964 Mark-III might've come with a left-over 1963 owner's-manual, when purchased earlier in the 1964-year).
The pre-1965 Mark-III never exhibited any clue of the 'Mark 3' title/name,, and not until the model-line came with the newly-added (for 1965) side-cover/tool-boxes, was there then any obvious clue to the model-name being altered from 'Mark III' to 'Mark'3' ! _ So (in my view), it's pretty-obvious that the Ducati-factory pretty-much officially changed the 'Diana Mark III' model-line's title-name to "250 Mark 3", beginning for the 1965 model-year !
And that stands to very-good reason, as the 1964 to 1965 model-year change-over then exhibited major-changes of that model-line,, as that was exactly when the old Mark-III top-end was eliminated & replaced with the 'Mach-I' top-end !
" the owner believes it has no AAU in place
and I note DCT-Bob stated that the 18 degree unit should function fine in there without modification. Do I have that correct? "
____ Yes... after installation, ya just have to reset the static-ign.timing (from about 39) to 20 ~ 23-degrees BTDC.
" wanted to check if the ID number AA367B is the correct 18 degree magneto unit. "
____ I never memorized those designation-numbers but, ya can discern the correct AAU (for the energy-transfer type ignition) by noting that it's points-cam's lift-lobe only spands for about 1/3rd of it's total 360-degree duration, (where-as the battery-powered AAU-type is pretty-much just the opposite).
__ Here's a link to what the one you want should look like...
viewtopic.php?f=3&t=757&hilit=AA367B#p5214 And here's a link to another picture showing the AAU which you DON'T want...
viewtopic.php?f=3&t=757&p=6863&hilit=AA367B#p6863Duke-Cheers,
-Bob
