Have you tried to swap the diaphragms between the carbs? It has been noticed that some times they might get hard with age and reluctunt to move properly. Do your slides rise in tune with each other?
Also, a long shot as I don't remember if it is possible, but can you reverse the carbs for a static test?
Alternatively, find a friend with time and appetite and swap carbs.
How about the hall effect sensor that signals the front spark?
mousitsas screwed with this post 05-07-2012 at 10:56 PM