Well something has slipped, changed, broke or moved, just have to find what. Or something between the 2 motors is missing ?
When you said you had checked the accelerator pumps , you did this how ? On mine , it will shoot a stream of gas about 5 feet or more out of the manifold, mine may be rich.
Mag can be checked for spark with grounded plug, correct?
Like I said, when my Webers were on several motors (no magneto) turn my throttle 1/2 turn , it will light and run a few seconds every time I kick it.