DC;

... it MAY be centrifugal advance not returning (a timing light should show that easy enough when blipping throttle), or, as others have mentioned, it may be carb linkage not returning well...worn linkages jam up...also check return springs...if you have later SUs with throttle over-run valves, these MAY jam, although that is rare...check it out carefully and let us know if its IGN or carbs...I'm betting carbs, 'cause there's more to go wrong on old linkages...

Parts are available from hundreds of "parts carbs" out there...even new parts are available from a few suppliers...SUs, (being one of the few things the British automotive industry got REALLY RIGHT) so they'll hopefully never go out of style!!

Thanks for compliments on IGN article...SU article is almost ready for prime time...watch for it!

...gotta bolt!